We've had a sort of similar discussion here.

There are multiple aspects to this question.
Are those fun helpers? I bet they are, they're colorful, usually more intuitive than anything else. The authors had fun writing them, maybe learned something along the way (isn't it usually like that that those tools appear).

Is it necessary to rewrite some core utilities? Well, in a certain way because it teaches the author about the ins and outs of what is necessary to achieve a similar tool to a core one it may introduce them to why the utility is currently the way it is, or how they could help in fixing it.

Are those tools the must have for everyone? For each their own. I'd rather stick with core utilities for the simple reason that they are available everywhere but I don't have an issue testing something novel written in a fancy language.

NB: Your thread was moved from the community section to the shell scripting one.