What to do when the difference between your competitor and you is 1 function.?

I've been working on a SaaS app recently. The problem I've stumbled upon is that I'm not sure if people would pay for this if my competitor, Yammer is very popular, whereas my app is still being developed. Basically the only difference is 1 functionality and pricing(we're not an enterprise) Workflo is an easy way to collaborate with your team using a micro blogging platform. Workflo works on a very similar principal to Twitter. Our competitors include Yammer, Presently and HashWork. In the status updates, we let you post todo's, attach files to your status-updates, and direct messaging(such as @name: do this). With workflo, it's really easy to set a todo for your teammate, for instance: "@pg todo: Please see the applications for #ycombinator-project #next-friday" will set a todo for PG telling him to see the applications for the project with the name "YCombinator Project" by next Friday. I'm not sure whether I should continue developing it if the only thing between us and Yammer is that extra functionality. I've gone totally crazy on this project, to that point in which I looked at Yammer's design and thought, well I believe ours should look like this.