Frankly, I am not very sure about them. If you are considering the firm, you can give them a try and check how they work.
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: https://cftc.gov/MarketReports/financialfcmdata/index.htm
And I'm not sure about you; bot... 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