I've had my SatMap for a few weeks now and think it's an incredibly good device, though it has a few flaws and quirks.
It looks great, is of excellent quality and the buttons and joystick are easy to use. The screen is large and gives a clear image, though this can be negated by reflections from the screen cover. In bright sunlight you may need to press the backlight boost button for 100% brightness. For power saving you can configure the percentage brightness for when its not boosted.
One thing everyone comments on is the time taken to acquire satellites when it's switched on for the first time at a new location. It takes a few minutes but if you switch it on upon arrival it'll be ready by the time you're prepared to start your walk/cycle ride. It finds more satellites than my Garmin Etrex and hangs onto the signal much better than it when amongst trees (though the latest Extrex is said to better than the older ones).
I leave the SatMap's GPS switched on while I'm walking but set it so the screen switches off after 30sec. This saves on batteries and the display comes alive again at the press of any button. Leaving the GPS switched on means a continuous snail trail of your location is recorded, which you don't get otherwise.
The device is switched off (and on) with a single press of a button, which can be pressed by accident when you mean to press another one. If you switch it off by accident, the device will acquire the satellites quickly when switched on again and resume recording the trail. However, if the trail is later converted to a track and exported in GPX format to MemoryMap, the latter won't understand the way the track has been recorded in two sections. Luckily, that can easily be sorted by editing the GPX file - just remove the </trkseg><trkseg> bit which splits the track segments, and any successive lines showing zero elevation or other funnies from when the device was restarting.
I've found the SatMap's accuracy to be very good. I placed the device on top of a trig point, and when I zoomed right in on the 1:25,000 map I found the reported position was right in the middle of the trig point symbol!
The built-in electronic compass seems okay when stationary, giving a reasonably close reading to a standard magnetic compass. However, when I used the GPS-based pointer to navigate to a GoTo point, it wavered about from one side to the other of the actual direction. I ended up heading towards the middle position and that took me there okay, but it wasn't very inspiring.
Only a quick start guide is supplied with the device. A much more detailed user guide can be downloaded from the website. However, it concentrates on what each control does in isolation rather than telling you how to combine the features on a day out on the hills.
The supplied Lithium AA batteries lasted well, but would be expensive in the long term at £4 for a pack of 4 (the device takes 3 of them). I tried using 2500 mAh NiMh rechargeable AA batteries but after only a few minutes of using fully charged ones the battery level dropped from 4 bars to 3 then almost immediately to 1 bar, with a message that the system was shutting down in 30 seconds. In fact, the same quick change in battery level from 3 to 1 and shutdown happened with the Lithium batteries though at least I'd had a long period with 4 bars before that. I've now ordered the optional LiPol rechargeable battery which is reputed to be long lasting.
The Ordnance Survey maps, sold separately on SD cards, are available in 1:25,000 & 1:50:000 scale. I bought the 1:50,000 set for all the National Parks in Britain (which is good value), plus the combined 1:25,000 & 1:50:000 maps for the area where I spend most time walking. That gives me coverage of most places I'm likely to go walking, with more detail for the area I go to most frequently.
Despite some flaws, the SatMap is an excellent, easy to use and very accurate GPS with a full OS map capability, and I highly recommend it.