Haven't tried Mojo yet but I have tried Julia and it kinda sucked balls. Sorry Julia fans, but it did. My main complaints:

• It's a research language like MATLAB, so the emphasis is on repl's, trying things out etc. But the compilation model is like C++. When you import a package it spends like 2 minutes compiling it. I think it's supposed to cache it but the second time it was still like 10 seconds for me just to import a package. I believe they've improved this since I used it but still, huge red flag.
• 1-based indexing. Come on guys. Anyone using this is smart enough to learn 0-based indexing. It's like putting a steering wheel in a jet fighter because you worry about pilots getting confused by a joystick. Again, red flag.
• The plotting libraries (a core feature for this sort of language) kind of sucks. In fairness nothing comes close to MATLAB on this front. I ended up paying for MATLAB because of that.

There's also this article which has more reasons.

I am leaving it a while longer before I try Mojo.