In terms of rapidly getting up & running with projects, I think micro::bit fills a nice niche in between an arduino and pi. You can have a light blinking in a few minutes on an arduino, but not much more without add components. A pi can obviously do tons of stuff without any additional hardware, but you have to boot a full OS to get there. A micro::bit gets you up & running about as fast as an arduino but you can code more meaningful projects without any additional hardware.
It's a very versatile device. I paired mine with a LoraWAN Hat and it sits outside in my garden, in a waterproof (unventilated) case measuring temperature and light. It's worked reliably through heatwaves and cold, wet weather and only stops working when the batteries die. It's very tough.
