One element of your question would concern me; if an incumbent sees your success, they could easily add your unique feature. If it really is just that simple, it seems like a risky project.
On the other hand, if you also have a lower margin business model that your competitors can't easily match then that risk is mitigated. For example, you launch with free base product and $1+/month for extra features whereas they are $10/month basic. It's hard for a company to come down in price like that (see Innovator's Dilemma).
Of course there are other factors, but that one stood out.