The 1.6 gallon Flushmate have been fairly reliable. (This one works)
However, that was when they were made in the USA.
Recently Gerber, a longtime family owned business, has been bought by Globe Union of China.
Quality seems to have dropped some since they have changed manufacturing.
We recently had one home where we tried two of the Gerber 21-312 elongated Ultraflush toilets, and could not get a good enough flush to satisfy the homeowner.
After two different toilets, we tried another brand, just to make sure it wasn't the house plumbing.
We were able to get a working flush with a Toto Drake.
When Gerber were made in the USA, we didn't encounter problems like this.
The dual flush by WDI has had handle problems. (Not Recommended)
When the handle quits giving a choice between the two flush types, most homeowner return the tank.
40% of the WDI Ecoflush tanks have come back for replacement.
Gerber says it has a 3" trapway on it's literature.
Not really, more like 2" at the max.