I bought a GTA5 Key (~30$) from this service yesterday, and got an invalid key.
It says on their website that they would reply within 24H but after reading up on some more reviews I get why that has not happened yet.

I have contacted them through email, and I am about to send them a PM on here.
Hopefully this will get resolved.

There is also no registration button on the website, but you can register by asking for a new password.