Using WPMU for restricting access to premium content

I’ve been considering using WordPress Multisite for an upcoming project. However, I’ve been reluctant to commit to the idea because a particular flaw or “feature” that I’ve noticed.

When I have a multisite network of, say, only 2 different sites (Site A & Site B — excluding the main “network” site) … I’ve noticed that when a user registers for a user account on Site B and then logs in to Site B, they can then navigate over to Site A and interact with it as though they are a registered and logged in user of Site A. That’s probably fine if it just allows that user to post comments, etc. But — what if both Site A and Site B feature premium content that should only be accessible to users who are registered for that specific site?

In other words .. if I want the registered users for Site A to only be able to access the premium content that’s on Site A and for the registered user for Site B to only be able to access the premium content that’s on Site B .. what’s the best way to accomplish that?

I’ve started tinkering with the free “Paid Memberships Pro” plugin. I’ve confirmed that it does in fact work … that members who register and log in through Site B can NOT navigate over to Site A and then access the premium content that’s on it. But there are a couple of things that I don’t particularly like about it. Namely ..

1) It ties into the existing WordPress users listing rather sloppily, I’ve noticed, where if you delete the WordPress user, the duplicated “member” account does NOT get deleted, and there doesn’t seem to be any way to delete it via any of the plugin’s admin screens.

2) Logging in to a member account for whatever reason requires that the user do so via the wordpress admin login screen, instead of through a login form that’s on the front end of the website.

I’m just wondering if there’s a better solution than the free Paid Memberships Pro plugin I’ve been experimenting with .. or if there are any known fixes/patches for the annoyances I’ve indicated regarding it. Please advise.

Thanks,
– Yvan