I have all that in my watch. The compass is roughly equivalent to a button compass. It'll stop you walking round in circles, and make sure you are walking along a road in the right direction and not 180 degrees wrong. It's not really for precision orienteering. It's better than nothing, and it's main benefit for me is that I always have it on me, even if I wasn't planning to get lost.

I can't really comment on the barometer. All I've done with mine is compare it with a GPS height. In theory it might help you figure out which map contour line you are on, but only if you calibrate it first to a known reference, and even then the weather has to be relatively stable.

The purpose of the thermometer is to help the device correct the other sensors for temperature variations. It doesn't have much direct utility for the end-user.

Being solar powered is a big benefit for a gadget watch like this. It means you can use the features without worrying about bringing closer the time when you have to replace the battery; the features become free to use. MostlyHarmless mentioned a concern about it not being charged due to not enough sunlight or something. That's not been a concern for me. With normal wearing, my watch's power indicator has never dropped below "high". So this contributes to the "always with you, always available" vibe.

PS My watch is a Casio PRW-1500. Great if you like gadgets, but not the cheapest way to get a compass.