EDIT: Removed most of my complaints because I misread the page.
The ARM Evaluation System was the first product that anyone could buy with an ARM processor in it. It wasn't for normal end users though, it was designed to allow developers to build ARM software before the Acorn Archimedes workstation was released.
It attaches to the BBC Micro, which supported external processors via the "Tube" interface from the outset. Faster 6502 processors, and Z80s for running CP/M were the usual upgrades. Later you could connect a 286 to run DOS.
It was. They had one of these at LVL Rocom, computewise it totally blew away anything that I had gotten my hands on until that point including some really nice mainframes (i/o wise obviously not). 3 MIPS in something that very comfortably fit on your desk. Now it seems incredibly slow but in 1986 it was unbelievably fast.
Part 1: https://arstechnica.com/gadgets/2022/09/a-history-of-arm-par...
Part 2: https://arstechnica.com/gadgets/2022/11/a-history-of-arm-par...