I just got mine and it’s pretty slick. It’s ideal for long-term use cases, where you don’t want to hassle with changing the battery every year or so. I’m using this one in my RV trailer. For some reason that tag’s battery drains quite fast (twice a year) and it’s a pain to replace it.
This device is much larger than an AirTag (think large coin versus thick AppleTV remote) and since you remove the metal back of the AirTag to install it into the device, you’ll need to keep that someplace safe if you ever want to use the AirTag as a regular tag again. The four screws are a pain to install, but then the whole point is this lasts for years so it’s not like you need to open it often.
People on Amazon were complaining the case is “cheap plastic” but it feels solid to me and imagine it has to be plastic to allow the AirTag’s radio signals to penetrate.
Bottom line: useful if you’re tired of replacing AirTag batteries frequently.