I have a securities background and they appear legitimate, but I would be cautious. They offer a very low money market rate, so they are definitely making a high spread on cash held in accounts. If you trade frequently and don't hold cash, it could be worth it. Otherwise, I would use one of the bigger discount brokerage options for a diversified (including cash) portfolio.
If you are buy and hold (trade infrequently), then I definitely would pick an outfit with better customer service and utilize them.