The Gecko 201 is a midget GPS system, handy to take almost anywhere. It has slightly improved memory compared to the Garmin Etrex and has WAAS error correction for better accuracy.
There are two problems everyone talks about with the Geckos. The on-off button and battery life.
The on-off button used to have a habit of operating while the unit was in the ruck-sack or pocket meaning you either didn't record your track or you ran your batteries down. The newer models (including the one I bought in July 2005 from Amazon) don't seem to suffer from this problem. The button is not very pronounced and has a raised ring to protect it from being pressed accidentally.
Battery life is a problem with all GPS. With tiny AAA batteries you would imagine that the Gecko would be awful. However with a pair of 800mha NiMH you can between 6 to 8 hours continuous use in power save mode. Get a pack of 4 and a fast charger and all is well. From experience battery life really suffers in the cold - for example skiing and there is a tradeoff between keeping the GPS in a place where you get a good signal and keeping it warm.
If you want to use it on your bike (instead of a trip computer maybe?) there is a handlebar mount. This works well, even mountain biking but you have to unscrew the mount to get at the batteries which is a pain, especially as you will be changing them reguarly.
Reception is okay, except under dense trees when it gets a bit confused.
I would not consider the Gecko 101 - no computer interface. The Gecko 201 has pretty much everything you need in a basic GPS and can work with computer mapping software. The improve memory makes it a win over the similar Garmin Etrex, the only thing the Etrex brings is the possibility to use high capacity 2600mHa AA cells.
Really it is just the handlebar mount and shortish battery life that stop me giving this unit 5 starts.