you get that membership only if you want to control the trainer from your phone or click the buttons to activate things inside the trainer, otherwise you just have to press keys on your keyboard which is perfectly fine. MrAntiFun has created hundreds of trainers, newer games that are updated more often are obviously gonna break some trainer functions and he needs to update the trainer. Just be patient, he can't update a trainer as soon as an update hits, maybe he is working on something else.
WeMod has many thousands of users, and since the app is free to download and use it has accumulated quite a large number of members and reviews. If the game is too old maybe he won't even bother updating it anymore, you can vote to have it updated, if the game is old and enough people vote to update it, then he'll update it.
