We looked hard at caspio a few times but always found the datapages restrictions and subscriptions per user the initial barriers.
Then using Knack the development-to-use time has been pleasantly very short, the built-in user pages & records restrictions really easy to use without complex filtering, and the benefits of simple JavaScript & CSS editors all a pleasure to use.
I'm sure there's users out there than have more experience with Caspio that can answer your other questions.