I rode biopace chainrings on my good weather fixed gear bike for two years, and I liked it; especially on hills.

I adusted my chain tension to the tiniest amount of slack that felt comfortable to me, at the chain's two tightest positions, and this gave me about 1/2" slack at the loosest positions.

From memory, I think I did this with the two extreme's of biopace rings, a 53t ring and a 39t ring; one of which gave me 82 gear inches with a 17t cog; and the other of which gave me 60 gear inches with a 17t cog.

Shimano tuned or shaped these two rings for maximum efficiency or comfort at two different rpm's, and I can't remember the details.

In the end, it takes the same amount of energy to do the same amount of work, regardless of the shape of the chainring.
However, the biopace chainrings did feel more comfortable.
Suprisingly, initially, I could spin faster with the biopace; and the non-round biopace actually felt more round than a conventional round chainring.

I don't remember why I abandoned the biopace chainrings.
I still have several of them hanging on my garage wall.

I do remember that I couldn't get the biopace chainrings to run as quietly/silently as my round chainrings (I like a dead silent chain), as the chain would make a little noise, twice per crank revolution, as the chain went "up" the ramp of the increasing portion of the biopace ring.

One can buy a biopace ring for less than$30, and, it makes a worthy and fun experiment.

To some extent, they work.
Subjectively, it feels easier to spin, due to the distribution of the effort, even though we know the laws of physics tell us it takes the same amount of energy to do the same amount of work.