I know it sounds bad, but it makes sense. They essentially buy your sats at a 50% discount. It works like an auto lien loan, except automobiles tend to depriciate and bitcoin is NGU technology.
If you pay them back with interest, you get your sats back, assuming they won't rug pull you. I remember hearing about Lendn at Pacific Bitcoin 2022 while FTX colapsed. They're still around, so at least they have a good track record. The risk of rug is non-zero however. That's why it's not a good idea to borrow more than 5% of your stack.
Even if theynare above board, Lendn executives could be deemed illegal and the sats get sucked into the SBR. It's why nothing beats staying humble and stacking sats.