I find them to be useful, yet a bit unwieldy due to the diminished sizes. I have personally purchased four sets of the last five releases.
The price is very affordable, but it comes down to whether you as a DM or player want to justify spending that much. Personally, I'd rather use Dungeon Tiles than drawing out the map on a featureless markerboard. However, there is something to be spoken about pre-drawing your maps on 1x1 grid paper they offer in massive sheets at Office Max. A pad is around 35 bucks, which I've used in conjunction with the Map Tiles.