Unfortunately there are 2 serious drawback to this: 1. Non replaceable/rechargeable battery 2. No support for directional tracking using U1. It’s just the standard find my networks Bluetooth beacon and the ability to emit a sound. Not the local directional finding available with AirTags.

That doesn't use U1 or U1-like tracking, though (can only beep, no precise finding like AirTag).

yes, it is 2.4 mm thick, vs an ordinary ccard that is about 0.8mm thick - so the thickness of three credit cards, not exactly meeting the no-bulge goal