Love it.  I first bought the 1.5" model but it wasn't enough cushioning
This thickness works great for my stationary bike and also for my riding mower.  It greatly reduces strain and absorbs shocks when mowing.  I'm ordering another as I'm tired of switching back and forth and it gets dirty on the mower.  It's expensive but my back needs all the comfort it can get and this product has "quality" written all over it.  I first bought the 1.5" version, and it didn't do enough for that but I use it on my  den chair where it is the perfect amount of additional cushioning without any sense of movement that I get with the 2" model.  I might also add that I weigh 220 pds and it still works for me.  I've read other reviews where it didn't work for heavier people.  For my stationary bike I used to use three conventional chair pillows and this surpasses that.  I just tried it out on a hard floor surface and it does flatten out at my weight.  Both my bike and my rider mower have some degree of built in cushioning.  Mine measured just under 15" x 18".  A larger size would be preferable.
Rating: 4 stars