I developed with Grails some years back and my experience was not that good. It is indeed impressive how fast you can produce a functional first version of an application, but there is price to pay for it. Groovy/Grails contain a lot of (dark) magic which is hard to understand/debug/refactor at times. The generated code (which makes the fast progress possible) needs to be rewritten sooner or later in my experience, so this is not a big time saver in the long run. In my opinion Groovy is just not a good programming language. Kotlin is much better and would also prefer the good old Java.

My personal impression is that Grails lost much of the momentum it had years ago.