Chuck,
I have a G-4....all I can say about the plastic is that it strikes me as being thin. I am totally paranoid about dropping the cup.
That said, the thing works. I will paraphrase a quote from RC....The thing pulls out tons of gunk, but don't play football with it.
I don't have a technical, scientific explaination, but the Aqua C 150 I replaced it with struck me as beging a lot more solid. I banged that guy around a few times without incident. The aquac was just a little too small for my system (it was one of the older models) and it is a PIA to clean.
G4 is nothing more than a big tube with a cup on the top. a la euroreef. IMHO, it's all in the pump and impellar.
As far as how long the plastic will last...I don't have a clue. I bought mine from a guy in CT who said he had it for a little over a year. I stuck it in the tub with some (OK two gallons of vinegar) and water and let that baby go for the day. Latte type foam
. The guy didn't clean it very well. (OK not at all). I figure it was pulling out all the stuff stuck (read growing) on the side of the skimmer. By the end of the day it was crystal clear. Almost like brand new.
I know Ray was looking at buying one, but I think he is going with a Euro-reef 12-1 by the looks of things in the selling forum. Drop him a PM and see if got some other info on the G6. I Hope this helps.
-Linda