The first thought that popped into my mind after reading your question is about protecting your market. If you expect this product to be highly profitable and

The first thought that popped into my mind after reading your question is about protecting your market. If you expect this product to be highly profitable and these other companies already distribute the software with other services, they might wise up and sell it as a separate service. If they were to unleash a feature-rich product on you with their brand image, you may find it difficult to handle. That being said, the fact that they have not done this already might imply that it's not highly profitable. That might be ok for you if you just want to have a smaller-scale profit with a niche audience. My second suggestion is simply to talk to people, find anyone and everyone who might be slightly interested and see if you can shoot them a personal email, tweet, etc. Most people who would get value out of what you offer would be happy to hear from you at least once. I've been doing the same with my side-project, Sparkmuse, and the responses have been both extremely helpful and surprisingly interested.