Mark blogged about our recent release of RIFE/Crud, but sadly his blog doesn't allow comments, so I'm replying in a separate blog post.
Rife CRUD scaffolding customization does not look nearly as flexible as Ruby Rails scaffolding, but that is fair: Rife does its scaffolding at runtime so there is no code to tweak - different than Ruby Rails where you can edit the generated .rhtml, Ruby controller, etc. files.
It depends on what you categorize as flexible, all distinct functionalities in RIFE/Crud have been extracted into dedicated methods in the RIFE element implementations (components). You can thus easily create your own element, re-use the automated logic and inject your element into the auto-generation logic. The benefit is that you don't modify the automatic behavior and still can benefit of library upgrades and bug fixes. You can of course also replace an entire element by your own.
I like the superb runtime performance of simple JSPs (with custom tag libraries) but there is no reason to believe that the runtime overhead of Rife and Rife CRUD scaffolding would be too bad
The performance should be as good or better than JSP. All auto-generated views are on-the-fly compiled to byte-code and loaded as regular Java classes. You thus get all the benefits, agility and performance.
Thanks for looking into RIFE/Crud, I hope you will look a bit further at all the rest that RIFE has to offer and consider it for a next project.