Don is always frowning upon Sub LLC's for the same reason he and his brother used to bad-mouth LLC's in general. Now that they ARE an LLC, I don't hear him bad-mouthing LLC's any more. Sure, some have gone bust, but so have firms of all structures.
The simple fact is that whatever the structure, unless you are trading retail with SIPC insurance, your $ is at risk. Period. End of story.
You can get financials but this doesn't prevent someone from blowing up the firm, no matter how much capital they have.
The sub-LLC helps protect Andover.
My advice is the same advice I received from an experienced floor trader when I was worried about my $ before I joined Bright in 1998:
Worry about making money, not about the solvency of the firm. It's much more likely you'll lose all your money than the firm will blow up and lose your $ because of someone's trading.