My fatbike was between stalling and slipping in the different parts of the stroke in deep snow or slippery conditions. Oval chainring improved that by smoothing out the torque to the wheel. I really like it. It also spins well.

I also added oval to my hybrid. It just seems to work better uphill and spinning. I couldn't tell that I'm I'm faster, just seems better.

Both have AB rings. Some other oval rings seem less ovalized, but I never tried one. When installing oval, I also went to fewer teeth, so I can't corroborate claims of more power.

Of course someone had to bring up Biopace. Hey, I tried a 3-gear derailleur from 1936 and it wasn't perfect. Therefore I conclude 12 speed XT doesn't work well.