Yes, SD don't do returns (or customer service). Once you've given them your money it's gone. I think Sweatshop are the same now - only credit notes.
As for the shoes, never worn them myself. I've seen alot around at Parkrun and other places, and from a cursory glance they look like "imitation" running shoes - i.e. they've copied the look and appear to have the same features as "real" running shoes. Whether they perform the same I don't know, but would doubt it.
Given shoes are the only piece of equipment we use, I've never really understood the point of saving £20 over the course of 6 months or however long your shoes last. Why not just spend a bit more and enjoy your running ?
Not sure about a replacement shoe, but everyone has to offer you a refund if you order online - I think it's the law for distance selling. I believe you have about a month to return, but goods have to be in their original condition - I.e. don't tags off or wear shoes outside.
Forgot to mention I have a Fitbit - a "One" - that I was bought as a christmas present.
I was dubious about them, but have to say I'm pleasantly surprised. They and the app that displays the data are very well designed and they do make you think about how much you move around during the day. Having online challenges with people you know (my brother and his kids in the states for example) is good fun.
From a running perspective I think it would be pretty useless, unless you maybe went for the top of the range GPS model, but you can get a better "real" running watch for the money.