I'll start by saying that there are shockingly few AirTag accessories that wrap around an object, and the solution STM came up with is clever. It seems to hold well, and keeps the AirTag well protected and secure! But while it checks those core boxes, it's definitely not perfect:
* The belt-like design is clever, but you can only adjust the tightness in AirTag-size increments. Testing on several objects, there usually was one slot where it was a little loose, and the next slot would be nearly impossible to close. Getting a snug fit is really just based on luck.
* While it has the "SlackGrab peg" for excess strap, that doesn't help if there's more than one loop flopping around. There's not a great solution for this without some DIY!
* The maximum size isn't that big, and the minimum size isn't that small. Feels like there's some missed opportunity here.
* The STM logo embossed on the outside is kinda ugly, and the whole object looks rather homely.
I was able to make it work with my new fancy umbrella in a discreet way, so I'm happy about that, but it feels like this product isn't quite there. There doesn't seem to be a better alternative on the market, but that's not exactly a glowing recommendation.