Questions about Blidz

I ran across Blidz; I'm interested in your general thoughts and also have a few specific questions. Link to trustpilot page.

This might all be answered on their site, but what I'm getting from the trustpilot reviews is that they...umm...don't have the clearest documentation.

My questions are about duo deals:

1. Has anyone tried to activate a duo deal and had it fail unexpectedly? I know there's a time limit, but I'm wondering whether there are other unexpected reasons why it might not work.
2. If you get the duo deal price, do you literally get a lower price? Or do you simply get the difference between the full price and the discounted price in some other form, like store credit or a rebate or something?
3. I've seen a few deals for things I want for $1. Is this just a promotional thing for my first order?
4. Anything else I should keep in mind before trying a duo deal?

I'm not going to buy anything whose full price is too high, because I feel like it could screw up and I might end up paying full price.