Garmin Edge 705 GPS-enabled Cycle Trainer

I think that this is a well-made and useful piece of kit. As others have pointed out, the basemap is useless, so you'll need something else - budget accordingly. I use Openstreetmap, and there are now lots of regularly-updated versions of this which can be downloaded free, quite a few of which now allow "turn-by-turn" navigation. Personally, I prefer to plan my own route using Google Maps or similar (there are lots of websites which allow you to do this) and then upload the resulting course to the unit; I find the routes which the unit plans - which will vary according to the maps used anyway - are not always helpful. I find the unit accurate, although it does sometimes struggle under heavy tree cover or when between tall buildings. The trace is very rarely shown as more than a few metres out, but the current sped can bounce around quite a bit under such conditions. I've only once known the unit to completely lose its signal when out of doors, and have used it for one year / 10,000 miles. Even then, it regained its signal within thirty seconds.
You'll probably need to be a bit of a geek to get the best out of the Edge 705, but if you want the maximum amount of data (most of which is accurate; the altimeter is better than the old Avocet I used in the early 90s, and the heart rate monitor is as good as the £300 Polar Sport Tester I had at the same time, for instance) then I'd recommend it.
I'd previously mentioned in this review that buyers should avoid the 4GB SD card which Amazon sometimes "recommend" from this page - it wouldn't work with the 705, and 2GB is generally adequate, anyway - but a recent firmware update claims to have sorted this problem out. I haven't put this to the test myself, however.

This device is just about as advanced as cycling computers can be. It will track your position and movements, record your heart rate and cadence (the speed you turn the pedals) and it will aslo give you turn by turn directions. However, the supplied map is only a 'base map', it does not have intricate detail at street level. It is very important that you budget for mapping such as Garmin's own 'City Navigator 2008'. The City Navigator software has street level and even postcode details which will enable you to either plan routes on your computer using Mapsource (free from Garmin) or to plan routes on the device itself just as you would with a conventional in-car Sat Nav.
I have a Garmin 305, too, but this 705 unit really does raise the game. I have all my favourite cafés and stops stored in the 'favourites' section, so if I'm ever out and need a detour, I simply plot a route to either a point of interest (POI) (again, there is a huge point of interest built into City Navigator) or navigate to one of my favourites.
There is also a topographical map available (with contours), but it isn't in the same league as those available from Memory Map and Anquet.
My advice is to buy City Navigator 2008.

Summary

An expensive bicycle computer and training aid, with limited satnav and off-road navigation capabilities. Think carefully before buying this. When compared with a cheap bike computer you are paying a premium for the ability to collect and record speed and position as well as altitude, heartrate and cadence information (the latter at extra cost!). Compared to a typical satnav you have a sunlight-readable screen, long battery life, and a simple bike mount.

The unit is small and only 110g without mount. It seems fairly robust, but it's only a matter of time before the flap covering the USB port breaks off.

Display

Small but easily read in sunlight: the brighter the light the better it is. The backlight is needed only for shade or dark conditions; and turns off after a while but can be turned on again by tapping the stick or pressing a button. The light also turns on when giving directions so navigating at night is theoretically possible. Although in a recent night ride it would sometimes beep without turning on the back light (I didn't work out what it was indicating).

The colour choices could be better as the route line doesn't always stand out from some roads.

Training

Excellent. The ability to record every aspect of your route and then display it as a map, table and graph is very entertaining. More useful is the ability to compete against a past version of yourself much like the ghost car in a car racing game. I'm not a great athlete, but even I have been encouraged to push that little bit harder.

Mapping

Poor. On my first ride with the city navigator maps I was asked to drive down a one way street and make an illegal turn. My Tomtom had both of these correct. The Open Street Map mapping is patchy, but more useful for cycling as it includes most trails and paths that a cyclist rather than a car will be using. And whilst with both Tomtom and OSM you can easily update the maps; I don't know how to do this with Garmin. It is now possible to get routable OSM maps, which are painless to install. However when routing in cycle mode it often acts strangely, taking you off and back on to a straight road for no particular reason. It performs better when set to car mode, but then you lose the ability to easily select off-road navigation.

The OSM maps can fit in the internal memory, or be put onto a standard micro SD card.

Routing and Guidance

Often useless. The unit is very reluctant to realise you have strayed for its route (which is unavoidable due to the poor mapping). It will continue to imagine you are on route even when you are two or three streets away. Consequently, when it enters a zoomed-in display during a turn you may find that your position is actually off the screen. The guidance for a turn is typically a little after the turn and it is possible to miss a turning even at bicycle speed. There is a countdown, but this is not that helpful in the dense side-streets of London as it counts to zero after the turn. This is also a criticism of other Garmin satnavs, whereas Tomtom seem to alert you in good time.

If the device does finally realise you are well off-course the recalculation of the route takes too long to be useful. By the time it finishes you may be off that route as well. During the recalculation the unit locks: you can't turn on the backlight or start or stop the timer, which is very annoying.

Software

There is no Agent similar to that of the 405. Uploading tracks is a manual process, which you have to do twice if you use Garmin Connect as well as Garmin Training Center. Both these packages need improvement, but are reasonably serviceable. The biggest pity is that GTC doesn't allow you to see the summary data (pace, speed, etc) as an on screen table at the same time as the map.

Reliability

During one long ride the internal memory of my unit became corrupt. GTC reported not being able to load the workouts from the device, but the record of my trip was silently lost. Luckily I had the resources to repair the filesystem, but not recover the data. Garmin need to make available a utility to reformat and reinstall the whole device in case of failure.