Performance is definitely worse than in iTerm or gnome-terminal, but it's improved a lot in recent Upterm versions, and we plan to improve it further. I'd say it's good enough, but you can try yourself.

Recently there was this terminal performance test https://danluu.com/term-latency/

The author says that the most important things are typing delay and how quickly you can Ctrl+C a command, not how much text it prints per second. Upterm is good at both.