@Augderion
Don't give your account and login deets to anyone, ever. It's a fast-track way to getting your account yoinked and sold. To actually answer the question though, it sounds identical to the Mafias clients and the way the village system works with them. The products are stores on Mafias servers, off of IMVU's catalogue listing as far as I can tell. You 'use' the items (via code), in the same way you can 'wear' hidden stuff that everyone has access to with code commands. Think of it kind of like how the IMVU shop works, if you want to simplify things. You have full access to items you "try" in the shop, but only within that instance of the shop - they aren't in your inventory, but show up in the scene and your "Wearing" inventory while you try them.
I wouldn't be surprised if what they're offering is literally just using a Mafias client to put the poses/furniture in your room for you. Which is something you can just do yourself and then have full control over.
I don't know if it's recommended or not, but a lot of BM poses/furni will stay in your room. They just exist within that instance like all your regular stuff, despite not being in your inventory. I know some of the village products are timed though, so I assume they auto-delete or disable themselves after a certain period.