I used to have a 7G fast ferment, and got rid of it when I ran out of other things to try to stop my hoppy beers oxidising (I was hugely sceptical that plastic permeability could be the issue, but I ran out of their suggestions).
I still have the 3G one which is OK for half batches, but the trub dump valve is rubbish - is normally sticks solid so you can’t remove the mason jar, and one time removing the jar also unscrewed the valve inner so beer just poured out. I remained fastferment with quite a detailed breakdown of the issue and they just said “it must be adjusted wrong”.
For full size batches I now use an SS brewtexh bucket. I’d been looking at one for at least a year, and wish I’d just gone for it earlier, as I wasted a decent chunk of the price of it in wasted beer.
You can’t do a pressure transfer, but you can do closed transfers by purging the corny with CO2 (which I do by pushing Starsan out with CO2 from fermentation), then running a line from the corny gas out to the bung to backfill the fermenter with CO2 as the beer drains. I’ve seen somewhere that the brewbucket only holds 1PSI or something, but it seems to be enough for pushing starsan out of a corny, and when you pull the bung there is a reasonable his. Touch wood I’ve had no issues with oxidation yet.