You are right, there is no such thing as instagram proxie, all proxies, which are in fact IPs, are the same. What they mean by this however, is that they verify that the proxy works on Instagram.
The thing is that a lot of people spammed Ig to death and Ig unlike any other social platforms started to bad ips/proxies for a very long time. They have several degrees of banning, you can no longer create working accounts on some ips or you can't even access the IG site on others, i think there are also some intermediary levels that account for what you can do with accounts on those intermediary ips.
Anyway, getting back to the main idea, what some companies to is check that you can access the Ig site with those ips, nothing more. They can't actualy create accounts to test if the proxy works for that because that would defeat the purpose .
So the bottom lines are that:
- even with "instagram proxies" you might not be able to create accounts because they are banned at that level
- there are fewer proxies that work on instagram so some companies decided to ask more money for those, even if it costs them the same amount, they don't have access to unlimited ips, because there's actually a shortage of ipv4 so this is the solution they came up with.
that would be amazing, looking forward to reading it as I am sure many others will be