Much easier than a key, swapping disks is a breeze.
This has been under £6 in the past, but this is now, embrace the modern era.
Free delivery with prime, and rumour has it, free with a local depot drop.
Don't over tighten it, it does have a standard pin hole arrangement under the mechanism if you get it stuck.
I use mine with my cordless grinder, in the old days of a cable, I used to tie the spanner to the plug, meant I had to unplug it to swap disks. Safer. I'd still recommend taking the battery out when swapping, just in case you sever a digit.