The toilets that were installed at my house are Niagara Conservation Toilets.
I've gone around and around with experts regarding these low water consuming toilets. Now, with two years of testing on these low water consuming toilets, I just asked mama to honestly tell me how many times she has had to "double flush" her toilet, she said, "Less than a handful of times", and for myself, being 6-2, 240 pounds, I will double flush maybe once a week, just to remove "stains" in the bowl.
They may not be for everyone, but with water rates in California, I have seen a noticeable decrease in my water bill. Even with an occasional "double flush", you are consuming 1.64 gallons of water. For me, I personally like the quick and quiet refilling after the flush.
https://niagaracorp.com/resource-library/technology/