You're better off with Dorman than any discount broker, that's for sure. They've been around since 1956 and they've never had a problem that I'm personally aware of.
They're a CFTC registered FCM with a healthy balance sheet and plenty of excess capital:
First time poster; "not very sure" about Dorman...?!
Your generic "advice" doesn't answer the OP'S question.
I'm sure after a few posts you'll recommend one of your shady brokers