Expanding site to micro niche correctly

I have a facebook tool which has a good ranking on Google. I want to create a new page like mydomain/instagram-tool to expand the niche, but the thing is, the current URL for the Facebook tool access is mydomain.com/app/ and the instagram tool can be added on subdomain only, so it would be something like igtool.mydomain.com

Does this sound okay? or would it impact my current rankings for the Facebook tool negatively? Any advice is appreciated.