56-bit DES systems are at best marginal. They'll keep out the casual hackers, but are weak against an adversary who can spend just a few hundred thousand dollars. Recently this was demonstrated quite publicly. Clearly, the list of groups that can afford such devices includes most medium-sized companies. Use a well-known cipher.
Proprietary algorithms are generally worthless.
But they haven't had much public scrutiny yet, and the patent status of some of them is unclear. Buy from a reputable firm that understands security. There are lots of little things to get right, like making sure a copy of the key doesn't get written out to the swap area. As with any security system, that depends on who your enemies are. If your main concern is eavesdropping on the public Internet or at your recipient's site, you may be able to disregard some of these precautions.