I wouldn’t even call it withdraw, because Bull never custodied your bitcoin in the first place. They require you to put in either a bitcoin address, a lightning address or lightning invoice, or a Liquid btc address when you do a purchase. They then send the btc directly to the address you provided. The only thing they custodied was your fiat balance, but they never hold custody of your bitcoin. I love this model of pushing self custody.
And yes, supporting lightning, especially in today’s fee market is definitely a big plus.