I traded under a sub-llc once. Pro's- less capital required/cons-They wont hold your licenses, and you wont receive any 1099 or partnership for tax purposes
The problem historically is that some "sub-llc's" have simply walked away from leases, traders, and other financial obligations ans allowing the "main" firm to look as though they're stable and viable. Try to get set up with an actual exchange member broker dealer (and, yes, there are others besides Bright Trading). Don