redo might be simpler and more reliable, but shell isn't. And redo is encouraging even more work to be done in shell. Additionally, the redo version is more verbose and harder to read. While fancier tasks will make's version look horrible relatively quickly, they won't make redo's version look any better.
To this day I still don't understand redo (I'm just staring at it, and don't get anything) - haven't really read the internals.
With make it was easier for me to grasp the idea (or maybe I was simply 20 years younger then).
"as you can see in default.o.do, you can declare a dependency after building the program. In C, you get your best dependency information by trying to actually build, since that's how you find out which headers you need. redo is based on the following simple insight: you don't actually care what the dependencies are before you build the target; if the target doesn't exist, you obviously need to build it. Then, the build script itself can provide the dependency information however it wants; unlike in make, you don't need a special dependency syntax at all. You can even declare some of your dependencies after building, which makes C-style autodependencies much simpler."