Frankly I think its a pretty F**ked concept!
Apart from the mystery bag nature (something I don't want from my brewing) there are a couple of other problems that come to mind.
Carbonation, how much pressure do you think a plastic bag is going to hold? The industry standard I can find is a 95kPa burst pressure. Have to assume that the bag has some sort of pressure relief vent otherwise it would go well past that.
95kPa would give reasonable carbonation at say 4oC (typical fridge temperature) but what sort of yeast are you using. If you fermented at say 20oC and the pressure was 95kPa, then you put it in the fridge the pressure is going to drop, you would be lucky to get carbonation suitable for UK hand pull beer (around 3.2g/L).
Might be able to get a bit better condition if you used a Lager yeast (or a mixed yeast), have to be careful to cool slowly or even Lager would go dormant.
Recommending you leave the beer on the yeast for 30+ days shows a pretty poor knowledge of basic brewing. Over that sort of time frame you will get some yeast bite (autolysis) you will get some release of Protease A which will degrade the head on the beer as well as breaking up most of the other protein that provides a lot of the body in beer.
Every brewing textbook I have seen says after 14 days (at controlled Lager fermentation temperatures) there will be measurable harm. A commercial brewer making Lager in a CCV (unitank) would have within 28 days done at least 4 yeast/trub drops as standard practice.
I have a sample of a commercial Real Ale BIB (Bag In Box) on the back seat of my car, (
see Jigsaw) it is designed to have either fully conditioned Real Ale racked into the BIB then kept cool <12oC or conditioned in the BIB (see FAQ in link) but either way its very much aimed at Real Ale and the very low pressure involved.
Mind you at $10 I can see why you would give one a go, Looks like they are made by
Muntons (who make great Kits, LME & DME) note the price 24.95 GBP ($45.79 today) for 12L of beer.
Doesn't mean I haven't got my concerns, especially about contact time with the primary yeast.
Mark