Is it worth it? Does it increase speed, climbing, etc., or is it a waste of money?
I used elliptical chainrings on my road bike for several years. I currently have an elliptical chainring on my MTB (single chainring).
There have been a number of studies. Some conclude that it does improve performance. Some conclude that your body adapts, so there is no difference. Some of the Team Sky riders use non round rings, including TDF winners, so there is that.
My own personal experience is that they do help on climbs, on both dirt and pavement, but hurts on downhills, when on the road, because you can't spin as fast. Off road, I'm usually not pedaling that fast on downhills, so it isn't an issue.
When I had them on my road bike, with double chainrings, it took some fiddling around to get the shifting right, but had no problems after that. On an MTB with single chainring, there is no issue with shifting at all.
My advice would be to get one if you have an MTB with single chainring. If you are wealthy, you might try them on your road bike. You might like them, you might not. I've been thinking about getting a set for my current road bike, but don't want to spend the money.