SeedSigner is definitely an excellent open source project and one we recommend. SeedQR and stateless is a super awesome way to role as well. Buying and building it can be a bit too technical for some though and annoyingly (at least for us) doesn't use USB-C.

We're very fond of the Blockstream Jade too as their recent update now allows it to be used in a very similar way (which we cover in our review). The camera on the Jade is a little... finicky? and obviously the hardware is not general purpose, but it's super cheap (cheaper with our code) and has a battery in it which makes the air gapped, SeedQR experience really nice.

The Foundation Passport is also another super premium HWW that will soon support SeedQR style workflows too.

We'd recommend all 3 over any Trezor.