Question about social media schedulers

I am looking at a service called Postsked, I saw someone mention them in another thread a few months back for Story automation, but with Instagrams strict updates I wanted to ask if these type of schedulers are safe to use?

They are not an Instagram Partner, and I don't know if a scheduler that is US based would look good posting to my UK based accounts?

Before anyone offers an alternative solution - I do not want to use bots and VPS solutions, just need it for Story and Post scheduling.

If anyone has any experience with schedulers (non-Instagram partnered ones), I'd greatly appreciate a better understanding.

Thanks!