So far I am enjoying my 210. I had a 300 which I did like quite a bit(especially the compass). It became way too tedious to have to manually input all of the caches into it. As soon as the 210 was available I placed my online order. My experience is that it has very good reception especially compared to the Legend or the GPSMAP60. I tried those out before deciding that the Explorist series was the way I wanted to go. If it wasn't for the style of rechargeable battery that the 4/5/600 use I probably would have gone with the 400 earlier this year. However, for the money I didn't really need the SD card option and the AA batteries I thought were important for ease of bringing an extra power supply.
The annoyances that I've found are the 200 caches per file that you are limited to. You can have many different files of 200 each, but only one file can be selected to display on the map screen at a time. That is probably my biggest gripe and that isn't that big of a deal. There are other things too about it's firmware, but those complaints are covered in the Explorist bug's thread. The 210 I believe has the same file system and all of the same problems as the 4/5/600 units.
Having only had it for about three weeks I would recommend it.