I've used an elliptical chainring on a 1x8 and single speed MTB set up. It definitely feels noticeably different, and I always felt like it should, in principal, smooth out power delivery in low cadence climbing - so thought it would be good for my SS build.
However in practice when climbing off road you have to modulate your power output so much to clear terrain features and adjust for variable traction, that this doesn't really offer much, if any, help.
I wouldn't use one again if it cost more than a round ring (though I'd happily enough use one if it was cheaper!).