I've bought yarn from Simply Sock Yarn several times and never had a problem w/them.
Not familiar with the UK store.
Knitpicks also has good sock yarn; good prices, too.
I've knit a pair of socks with Maizy and don't remember the amount of elastic bothering me or being an issue while knitting. I have some other elastic sock yarn (Patons Stretch) - I haven't used it yet but even though it has less elastic in it then the Maizy, it seems more stretchy.
I do like sock yarn to have a bit of nylon or similar. I've found 100% wool does not wear well. Sounds like you got some good deals - now to start those socks!!