I will add to your post that I extensively researched low flow toilets about 8 or so years ago, when I had to buy my first low flow toilet. The low flows have much improved since then, I think, but I researched extensively because there were numerous horror stories of all the low flows that didn't work properly.

I did learn from toilet studies (yes, there are toilet flushing studies, if you can believe that), that not all models of a brand are the same.

It seemed to me that in the ratings and other information I read, one-piece toilets don't generally work as well as two piece toilets. The Toto Ultramax is a one-piece toilet, and while I think it did fine in the toilet review ratings, it was a less pricey two-piece that consistently performed at the top of the studies. I think it was the Toto Drake, which is what I ended up getting. Not many, if any, of the Kohlers did well (that's because Kohler hadn't yet changed its engineering for less water...it just used the same toilets but reduced the amount of water, and that is apparently not the way low flows work; the large water toilets rely on the strong woosh of a lot of water to push things down and through. Low flows require a different engineering, since there is not the large amount of water.)

I wish the Kohlers had performed well in the ratings back then, since I recall they were prettier than the Totos, or at least they suited my style better. Totos looked very modern to me, which I didn't think suited my older house well. The toilet I was replacing had curvy edges at the bottom and around the tank. It was a true old fashioned high-water toilet with curves and a soft white (as opposed to the stark white that so many toilets are now).

I then bought a second Toto (I think it's the Drake). In the 8 years I've had them, I haven't had one clog or had to flush twice. They work perfectly. You'd never know they were low water, except for the slightly lower water level in the bowl.

The Japanese (Totos) have been using low flow toilets for many years, so they were way ahead of the U.S. on the engineering for them. But it's nice that there are more choices now.

Just remember....it's the model, as well as the brand, that's important, regarding performance.