Roku setup

[Boothby171]

I recently bought a used Roku through Craigslist.  Call it "Roku A."  When I picked it up, the previous owner realized that he had forgotten to reset it before selling it to me, but he thought about it for a minute, and said, 

"It's still got Disney+ and CBS All Access on it.  But you know what?  Keep them.  Go ahead and use them if you want.  No problem" *

Not one to look a gift horse in the mouth, I thanked him, and went on my way.

So Roku A is registered to his account.  I assume that his NEW Roku (Roku B) is also registered to this same account.  I also have another Roku (Roku C) which I have registered to MY Roku account.  Roku C is my "go-to" unit, except for Disney+ and CBS All Access.

So here's the question:

If I put Netflix, Google Play, Amazon Prime, etc., onto Roku A (the used unit I bought), do they automatically show up on his new Roku B?  Do the icons show up on his home screen?  Is he able to access those services through his Roku B "automatically," or does he have to activate them (which I assume he could not do)?  I assume that the icons probably show up, but that he cannot access them.

My concern is 1) the risk of "too many people watching" re. my Netflix, and 2) Him being able to make purchases through my Google account, since there are credit cards associated with it.  IOW: What's my exposure?

Notes:

1. Yes, I know that the typical approach here is to RESET the old Roku (Roku A), but then I lose those two premium streaming channels.  Which I'd rather not.
2. Yes, his credit card information is associated with Roku A.  I can only see the last 4 digits, but I have no desire to make any purchases or rentals on Roku A, nor will I.  

* I kid you not!

[DBDukes]

All Roku devices tied to his Roku account will have the same apps on them. If a user on one Roku adds an app, it gets added to all devices on that account (provided, of course, the device supports the app; some older devices don't support all the apps). If a user on one Roku deletes an app, the app is deleted from all devices on that account.

So, if he adds PornHub on his Roku, you get PornHub. Just sayin. If you add Amazon on the Roku, he gets Amazon. And, Roku has implemented single-sign-on that some apps use. Just as you're using his credentials because the device is tied to his account has those apps, and they implement Roku's single-sign-on process, if you add an app that uses Roku's single-sign-on, he gets that app on his device and it's logged in to your app service account.

Does that make sense?

[Boothby171]

Thank you.

I'm keeping my own stuff off the Disney/CBS Roku.

I have another Roku (a TV/Roku combination) that I have in my office that I just bought used and it had someone else's Netflix on it.  I wound up resetting that Roku and establishing my own bona fides on it.  My daughter has a 4-viewer Netflix package, so there was no downside to resetting it, and not being able to install my own Hulu and Amazon Prime licenses on it would have been a pain.

Thank you for the insight into the issue, though!