There's nothing about payments that requires testing client properties though. What you want is the ability to test if there's a corresponding payment, that has nothing really to do with the client's device. It just seems like irrelevant information, what are these "desired properties"?
You want a corresponding token with the request that matches a payment. And WEI seems like a strictly inferior way to get that instead of just... asking a payment provider for the token. What does my hardware/OS/browser have to do with a payment token?