I had the retrofit done on my 2018 MS. Have never once successfully charged at a non-Tesla charger. I'm not sure if it's me or the charging stations, which are somewhat known to be less reliable in general than Tesla's.
I got the $450 adapter for my 2016; There's one charger I really wanted to use and otherwise I think it'll waste space in my trunk. I still haven't used it at that charger but I did test it at a CCS1 charger; it worked though it was a terrible experience - the CCS1 plug is silly huge, the payment processing was terrible, and it charged pretty slowly.
I think they're retrofitting the existing supercharger network to speak both "NACS" (really CCS1) and the OG supercharger protocol. My car, with the retrofit, will be able to (HA! good luck believing it'll actually work) charge at an EA or other DC Fast charger setup, possibly. Non-updated OG S/X cars will just get an error (probably I will also, because these other DC Fast chargers simply don't have skin in the game -- they're malicious compliance).
L2 will be nice -- I'll not have to use the dongle to charge at public chargers.
I bought the adapter off the gray market when it was only being sold in Korea, and promptly ran to my local EA station to try it out. Of the four plugs, only two worked, and one of those was loose and would glitch out if I didn't hold it against the car by hand.
I haven't charged via CCS since. It lives in the car as an emergency backup, but frankly I wouldn't plan a road trip stop at a CCS station if you paid me.
