My take is that it’s a good start and important step towards fully de-leading the fleet fuel. There was a good article on AVweb breaking down the difference between the STC and ASTM approaches and the work that still need to be done:
https://www.avweb.com/uncategorized/eagle-and-gami-not-a-transparent-process/
If you own a plane, do you intend to buy the GAMI STC for it?
Do you have access to G100UL at your airport or in your area?
I don’t have access to it locally and I’m not an owner, but I would love to see adoption as quickly as possible. I’d suspect it’s going to have a lot to do with Signature and the like deciding to offer UL. I’m guessing adoption will be very slow and then gather momentum, but I’m still waiting on any word of it anywhere I might fly.
EDIT: and good article as always by Paul Bertorelli. I think it’s been clear that unleaded fuel has always been more about bureaucracy, liability, and politics rather than any remaining technical hurdle. It fits with my view that the FAA would legislate recreational piston GA out of existence if it were coming up today rather than being a vestige of history, and it’s a miracle we have anything at all to play with under their oversight.