For all of these watches, the altimeter is only going to be accurate if you set it to a know altitude before using it. Most of these watches come with many features whether you want them or not.
I have a Highgear Axis. It comes with compass, altimeter, barometer, thermometer, etc. The altimeter is nice, fairly accrate, and give you a nice little picture to show your ascent/descent, max altitude, total gain/lost etc. The compass feature is useless. I do find that the barometric pressure is nice to watch, as the watch correlates this to the weather (picture of the sun, clouds, rain, partly cloudy). I have found it to be an additional tool when staying out for a couple days. The thermometer is useless on your wrist, but I like to hang it in the tent to know just how cold it is before heading out. It lets me know what I should wear when starting out. There are also the basics, time, stopwatch, and alarms. I have not had any problems with battery life (first one lasted about 2 years). The only downside to the watch is that its very large. On the positive side, this means it can double as a dinner plate