Being able to drop into REPL and rewrite it is a super power. And while MicroPython doesn't tend to come with every library that Python does, you can generally install them via pip.
How fast is it? I'm curious because I've been debating trying it out for some relatively simple stuff with GPIO pins and MQTT (largely just reading some sensors, enabling/disabling some other pins based on those sensors, and submitting telemetry via MQTT). MicroPython seems a lot faster to get up and running with, but I'm concerned that on such a small device that it'll be prohibitive (but I'm also coming from a server background, so I may be overestimating how much slower these are).
It isn't slow. If all you're doing is reading, then the overhead will be pretty much the same as if you were using the Espressif SDK, because you'll find the bottleneck is I/O, not the extras that MicroPython provides.
A cold boot is slower, and takes a couple seconds, but after that most of the latency is comparable to if you were doing it with the SDK.
MicroPython is heavily optimised, and doesn't supply a lot of the mutable madness that makes CPython so slow. (For example, a for loop in CPython is slower than a list expression. In MicroPython, they're the same speed.)
Being able to drop into REPL and rewrite it is a super power. And while MicroPython doesn't tend to come with every library that Python does, you can generally install them via pip.