Boltz mainly offers atomic swaps from lightning to onchain and vice versa. That effectively means you pay a lightning invoice and receive the coins in your onchain address (and the other way around; send coins to an onchain address and get them back via us paying a lightning invoice). All of that works in a way that you don't give up custody over your coins and we cannot steal from you.

Boltz is running LND because it was more mature back in the day, when we started our node. Personally, I am running a CLN node. I gotta say, if you want to have the low level control over your node CLN offers and can get used to the less friendly command line interface, I'd prefer CLN.