Whatever you do don't get Gelert ones, not fit for purpose, rubbish, heavy/thick material too. I think I'll get some Exped ones for my next trip.
Do the Karrimor ones stay compressed and airtight / keep their seal without sucking in air like the Gelert ones? What's the point of a "dry bag" which doesn't compress your gear? If it sucks in air it can suck in water as well and not waterproof. You may as well use plastic bags. I think you get what you pay for with dry bags, I bought some other cheap ones off eBay which also turned out to be rubbish as well. Karrimor stuff is a bit hit and miss, most of it is poor quality IMO but I've got a cheap pair of Karrimor Summit trail shoes which are surprisingly good though, some of their stuff is alright.