How Does Hopper HQ work?

Hi Guys. I was looking for a robust fully automated Instagram Scheduler and ended my pursuit with Hopper HQ. It is in sync with IG's T&C and also does not use any private API. But I wrote to them and they confirmed that they use a virtual user who will use account credentials to post at the scheduled time -no sweat! But how can they cater to thousands of accounts and even more number of posts for 2 years without drop in quality? Please let me know if anyone can shed some light on this.

I just looked at it. Looks pricey but still effective. My clients are currently using Grum which does same thing however its around 3$ an account if you have a bulk amount of them.