Go does provide collections and iterators and such, so Cello is similar on that front. But, every modern language provide those things, and Cello collections don't seem any more Go-like than they seem Python or ObjC like.

Well written C is consistently faster than well-written Go. There are some dynamic runtime elements to Cello that could potentially hurt performance but I doubt it's a major factor.

I think Rust is probably the better modern language to compare Cello to, and I suspect they'll have similar performance. ObjC would also be a reasonable thing to compare.

But, for most things, they're all Fast Enough. Performance is probably not a useful metric. The reason I could see for using this would be modernizing an existing C codebase (though I'd be cautious about relying on something like this until it has a healthy uptake among developers), or when working in environments where only C compilers and libraries are available. If I were starting a new systems project, I would start with Rust or Go (or maybe ObjC if I ever had to work on Mac/iOS).

Mostly though, I think it's just a cool experiment, and educational.