On first appearance this site looks like just another site out there with records on, but on closer inspection you will see this is run by the book sellers Naval and Military Press. (Why naval isn’t military is beyond me!)
They list approximately 1 miilion records, but if you plan on joining a site like Ancestry or Forces War Records, you will find all the same records there, as these are simply from the rolls of WW1 and WW2, which all good sites will already have.
I’d also watch out for their credit system. This is one of my bug bears with most sites that force you to purchase x amount of credits, but then 1 credit buys nothing and it takes you a least 5 or 10 credits to do anything. Why not simply divide the credits sold by 5 if it takes 5 credits to do anything?!
My advice. There’s better other sites.