I've been using Bubble for a few years for a side project. I always thought I'd use it just for the MVP phase but haven't had a need to move off it yet. The big downside is speed - the home page takes 2.5 seconds to load even after doing all the recommended optimizations (Cloudflare, fewer plugins, fewer styles, etc).

If you draw the line and add all efforts up, is it worthy? I mean, it might be great to quickly draw the frontend, but if for the backend you must jump through a bunch of proprietary hoops, can you still feel some advantage to the entire package?

yes ... a lot.

scaling may be different but very efficient approach to getting to reasonable scale (perhaps 1000s of users)