I put Grouser OTT on a New Holland L160 shortly after we purchased it in 2013. Our land is very hilly and running only tires would frequently just spin on the grass or dirt. I don't think they cause any power loss. OTT do add weight down low to help with stability on the hills. They also add a little bit of protection to the tires from punctures from branches/stumps. We mainly use it for work with trees such as piling logs and branches. Occasionally small branches will get stuck in the open slots on the tracks, so need to keep an eye out to watch for that.
We leave them on all the time as they are heavy and kinda a pain to put on. When installing it works bests to deflate the tires about 50% to get the connecting bolts in, then fill the tires again.
We never drive on hard surfaces or lawns, as OTT will scratch or tear up the surface pretty good. It is stored in a garage with concrete floor, so we put down rubber mats used in horse stalls to protect the garage floor.
The only complaint I have with the Grousers is that they have a very noisy, high pitch squeak, when in dry conditions. When running in mud, snow, etc they are quiet. I have to wear hearing protection(good thing to do anyway) to filter out the squeak when operating. I tried oiling the track bushings and bolts, but it doesn't keep it quiet very long. We had Loegering OTT on our previous Lahman skid steer and those tracks were much quieter, but the skid steer was also about 1/2 the size of the L160 so a lot less track.
Here is a video of our skid steer with Grouser OTT