This is not aimed to become an Invision competitor. There are however people for which Invision is too much and only need a simple way to share and collect a quick feedback one something they've been working on.
Don't go after the generalist approach, focus on a niche where UX or design thinking is a growing area, own the marketing for it, and then you can move to another niche. Perhaps aim at social media agencies looking for creative approval from their clients etc, own a smaller market and grow out from there.