It sounds like a relevant use case but I wouldn't buy the service. Our designers already have similar avenues for getting feedback (including screen shots in Slack), so it's not a pain point big enough for us to pay for a solution.
Kudos to you for getting feedback from your target audience before building. More importantly, if the solution improves your workflow, build it for yourself. Good luck!
It's hard to know if it would simplify the workflow enough to be worth building, it would have to be incredibly frictionless to be useful. I like the idea of posting to a wider community as well, for those not in teams.
It sounds like a relevant use case but I wouldn't buy the service. Our designers already have similar avenues for getting feedback (including screen shots in Slack), so it's not a pain point big enough for us to pay for a solution.
Kudos to you for getting feedback from your target audience before building. More importantly, if the solution improves your workflow, build it for yourself. Good luck!