While I agree that you are experiencing some red flags, I do want to share my own experience with them. I have been working them, 1-2 shops a week, every week, for over two years. I have done a total of 194 shops for them, for a total of $10,000 in reimbursement value. Hands down, they have been my FAVORITE company that I work for, and I work for about 30 companies. Up until December, they paid more quickly than any other company, within just a few weeks of the shop. I have loved working for them.
But this was until two months ago, when they suddenly became slow with their payments. When I reached out, I was also told that the person who processes payments was out sick for weeks. She sounded horribly embarrassed. As far as I can tell, it is a fairly small company, although they currently have one very large nationwide client, in addition to restaurants in California.
I'm going to reach out right now to ask about the December payments, since I still haven't received them. But again, for over two years, they paid in a more timely fashion (and twice a month) than anyone else I have worked with. (And I average about $50,000/year in reimbursements/fees.)
I'll let you know if things improve for me, at least. If they do, I will absolutely continue working for them, as they were a delight until now.