That said, I have three points:
1) I would never start thinking about making a UI element by thinking about performance. I would build to my functional requirements, and then optimize if necessary.
2) I use this class that draws a button programatically, and I use it inside a UITableView, on a screen that auto-rotates. I have never had an issue, and I developed this code for early iPhones, in 2010. Can you comment on my code in particular, which uses a CAGradientLayer? I have never noticed any issues with this code in practice.
https://www.dropbox.com/s/5w938hx7ittzhc2/TripComputerButton...
3) I never thought about generating UIImages of various colors at runtime - that does sound like a cool technique. It would be nice if stylish butons were built into UIKit - that would have saved me fumbling early on.
http://a1296.phobos.apple.com/us/r1000/118/Purple/v4/56/00/c...
For this table, I also render the cells once and don't dequeue them, because I like to achieve the transparent, gradient effect for each table section, over the classic vertical lines of the grouped UITableView. https://www.dropbox.com/s/67xfol10c0kkqb2/TripComputerCellBa...
In the end, it is really great to have detailed knowledge of UIKit and CoreGraphics, so you save yourself time optimizing on the end, if you just know the right thing to do. And I think your comments about the accuracy of the blog's claims are righteous and a good addition. I envy your fundamental grasp of this stuff, and I try to keep learning, even as I fumble towards what I want.
If you're using a masked CALayer, and that layer's in a scroll view or is otherwise animating around the screen, there's a very real chance that you'll drop frames, just from that layer's off-screen rendering pass. Depends on how big the button is.
Certainly, though, if you need parameterizable imagery, you need parameterizable imagery, and so you can't load them from disk. But you can still make your runtime-generated images resizable!