While I was at a startup recently, I did all of my frontend development in Backbone.js, this app would do a lot better in that framework.
Also, the CI framework isn't all that great, I would have certainly used a different framework. Perhaps even Node.js (which is what I'm doing a lot of my development in nowadays).
I also would have looked for a marketer and devoted more time to the project. The market for this kind of product is very crowded, but there is a lot of room for innovation.
I'm curious why you would choose Node.js instead today. I've done a little Node.js work, and I would unequivocally use it again for anything that needs a fair amount of concurrency, or high volume, lightweight requests. Other than that though, the only advantage I see over other server side stacks is a slight mental bonus in using the same language on both the client and server? Are there any other major advantages you see over PHP/Python/Ruby,etc. stacks?
I don't think anyone's ever subscribed to a SaaS product because it used X technology over Y. I also think you're way too focused on the tech and the list of features, instead of selling a solution.
You can say all you want about invoicing being an over saturated market, but I launched a very successful project management product a few months ago. Focus on doing a few things very well, and you can do well in just about any "saturated" B2B space.
Also, the CI framework isn't all that great, I would have certainly used a different framework. Perhaps even Node.js (which is what I'm doing a lot of my development in nowadays).
I also would have looked for a marketer and devoted more time to the project. The market for this kind of product is very crowded, but there is a lot of room for innovation.