Seems pretty reasonable to me if it's as useful to people as it appears to be judging by the comments here.

Personally I'm willing to even pay a slight premium for non-subscription options too.

I find it's important to know what you're buying though; particularly if the thing it's targeting is changing rapidly, like an IDE for a modern language, or something else they know will be made obsolete in a short time.

A book on Android 1.5, or Kubernetes Pod Security Policies doesn't (didn't) have much of a future.