I've been using one from that site (I selected UK and Benelux tiles) since entering the world of GPS units at Christmas. It looks good on the unit, and I've certainly found no problem areas so far in the UK on it.
I tend not to use turn-by-turn routing on the unit though, preferring to choose my own route in advance and create a track of it and follow (navigate to) that track instead.
I also loaded the talkytoaster maps of the UK (routable with contours and their OS 50k style map). I also like the look of those, but the OS look and feel one is not as good for cycling (roads a bit thin, too much extraneous detail) as the non-OS look and feel version. The OS look and feel version is great for walking though.