44 bits of security is not “pretty good”. The post author used Python, but anything more performant would result almost real-time decryption.

There are no performance implications of using a proper 128 key because they are doing AES anyway. If they were resource constrained and choose a variant of TEA encryption due to constraints, it would be understandable, but no, the encryption is implemented in hardware.

There also seems there is no message authentication, a rookie mistake.

44 bits is horrible obviously, but maybe it's fine for this use case?

The attack vector is: an adversary can get close to your water meter and after brute forcing the key, wirelessly read the numbers they could have just physically looked at the water meter to read anyway.

Meanwhile the device owner can decrypt the signal and locally get access to their own data without being tied to the cloud or a proprietary vendor app. I think that's a win.

>44 bits of security is not “pretty good”.

Hey, that's 4 bits stronger encryption than DVDs, and it's only like 30 years later to get those additional 4 bits