I mean, if they already have Bitcoin, just show them the Phoenix wallet, have them make a lightning transaction, and if they don't like it after that, then they just have their mind made up for whatever strange reason and your time would be better spent elsewhere.

If they've been holding for less than probably 4 years, then they're probably still trying to trade instead of DCA, so you could show them this:

Kraken supports lightning network. https://blog.kraken.com/post/13502/kraken-now-supports-instant-lightning-network-btc-transactions/