Legality of WoW Private Server

So I've been wondering, is it actually okay to play on a World of Warcraft private Server. I've hated what the game had become and so I would really like to game back on an expansion, or even to play at a point where I've never even been able to experience it.

 

Also if anyone is interested, maybe we could make a Tek guild on the private server that I've found. It will also be a horde guild!

https://www.molten-wow.com/

Its against the Blizzard ToS so if you have an active wow account and they find out they can ban your account but im not sure what they could/would do to you if they found you playing on them as far as i know they just shut down the servers

When i used to play wow i always ventured between private and the offical servers and nothing happend

But most the private servers ive come across either have ridiculous top levels, completely OP donor gear, a million times xp but low gold rate (personally it annoyed me too much to play on) Or they quests/dungeons are fubar or generally laggy as hell or terrible communities