I had a 2015 M5, it was easily one of the best Macs I've owned. Ultra-ultra-ultra portable, I had great battery life with mine, and it was as fast as my 2013 Macbook Pro. I used it as my daily driver for 3 years before I got a new job (and a new work-issued laptop). Paired with a monitor that provided USB-C power (there were a few at the time, I got one of the Philips displays) it got me through several sizeable web dev projects. It's only just been retired, as the battery finally made it unusable, and now its logic board (and 2 others: my wife's 2015 Macbook and a lucky score on eBay) are part of a 3-machine cluster with Ubuntu installed, because why not... each one just has a USB-c power/ethernet dongle plugged into it, and I've got a little compute cluster that punches way above its weight for the amount of space it takes up (and the power it consumes, which is very little, especially with the display removed).

If you could buy SBCs based on the m5, I'd eat them up.