You have an interesting product. I like the simplicity of it both in terms of ease-of-use and ability to make it more secure later. Are you intending to keep this thing going or build it up for an acquisition? If the former, I might do a consult with you on bulletproofing it in the future once its grown enough to justify the cost. If you like that, just keep the implementation well-documented, modular, and basically easy to reimplement if necessary.