Do they adequately explain what L-BTC is and how to get the "real" BTC out of it? I'm not sure what's the point of selling L-BTC directly other than to mislead users into buying something they don't need. They could sell BTC and allow to "peg in" if someone wants to.
Hmm... I had to download their wallet, but I don't think they explain as much as they could/should.
You can download the app, go to the "Exchange" tab (the one on the OP), tap Buy L-BTC and just put your credit card details. I do agree they should have an screen explaining that L-BTC is not the actual on-chain BTC and that they may not be able to spend them to unsupported third-parties.
They do have an "Liquid 101" FAQ on the "Profile" page (last icon on the navbar), but it's not really intended for beginners.