1. An American Standard 6.0 gpf toilet will NOT flush properly with a 1.6 DuoFlush unit in full flush mode.
2. VERY few users will bother trying to figure out which way to flip the handle for a full flush, so there will be a lot of partial flushes, if not ALL of them. It will be like the American Standard "Vent-a-Way" systems. The users seldom, if ever, realized they had to operate the handle in the reverse way for it to function, so it was NEVER really used, even though they paid dearly for the feature on their toilets.
3. I hope he tightened the nut on the bottom more than "hand tight" the way he said he was going to tighten it.
4. That tank to bowl gasket will not always seal properly.
5. When the handle breaks, which most plastic ones do, I hope they are still in business, and the customer has more than one toilet to use while waiting for the new one to be delivered.