I’m surprised you don’t mention the brand and model of the SSD being used. Since this M.2 2230 format isn’t as widespread as other M.2 sizes, it’s quite restricted what you can get. At this moment I only see a Toshiba TLC (BG3 series) and I would like to compare this to what’s inside the Surface Laptop 3.
Exactly! Given the amount of effort they put into shrinking (or folding) certain parts, it’s great to see they’ve put in the same effort to not make it harder to repair. That any modern smartphone will never receive a 10/10 score due to the design choices is acceptable, so I’m happy to see there’s still a reasonable way in. Not like some tablet/laptop hybrids that are horrendous to even open up; yes I’m looking at you Microsoft!
I think we can safely assume it’s the global A1901 model. Both other models are country specific according to EveryMac.com: A1865 for China and A1902 for Japan.
Manufacturers that don't say it's compatible, just haven't tested it. You just have to pay special attention to the notch(es) on the connector. I had a 512 GB SSD lying around, but it had two notches at 1/3 and 2/3 (M.2 B & M notches) instead of the MacBook's notch that's somewhat in the middle and is NOT a standard of the M.2 format.
Yes, it's mentioned on the top of this page. P5 Pentalobe to be precise. I didn't have one either, so I bought one from iFixit and that works fantastic. An absolutely precise fit, which is important especially when you might open your MacBook a couple of times during the years you own it. Not using the correct tool might do more harm to the screws than you want! I once had this with a Lenovo Yoga 3 Pro, which has Torx screws (T4 I think) and I used cheap Chinese quality tools, with the result that both the tool and one of the screws are damaged.