They will invite anyone/class/spec to fill spots and then once their players decide to show up they will remove you from the raid for no reason, no explanation just a blind removal and screw you over on your weekly Mythic Raid ID.
Sadly we wiped twice on the 3rd boss so not only do they screw players over on their other weekly raid ID they screw you over on the Vault as well.
Avoid the guild and these players.