Most people that install the 1.ogpf version just love it.
However, the reason is that most people that order the 1.0gpf version are very interested in saving water. They are mentally-prepared for a smaller water spot, less rinse, less bowl refill, etc. Accordingly, they are amazed at what Toto can do with a gallon of water -- and it's pretty impressive! There is adequate rinse, an adequate water spot, and a very-effective flush. However, it is a noticeably-different experience than with a 1.28 Toto.
Toto managed to cut from 1.6 to 1.28 in a way that makes (on the Original Drake at least) almost zero noticeable difference. But from 1.28 to 1 was a much-tougher engineering assignment. They pulled it off, but you do have a smaller water spot and less rinse, because they prioritized a good flush. The reduction in water has to come from somewhere. But if it is important to save water, then it's amazing what Toto did with a more than 25-percent reduction in the amount of water used.
Here's the 1G in action. The only reason there's anything stuck to the bowl is that the person used old avocado for the video, and let it dry on there. (She said so in the comments.) If it were not dried on there, it would have been removed in the flush. She loves, loves, loves that toilet. But she also says that her primary goal was to save water. That the thing works amazingly is secondary.