The answer to your question is NO. There is no simple way to chech this. There is a difficult way to test that in your particular test scenario RFC6979 is used.
One more comment: If I understand this correctly, the Trezor use case for signing transaction never reuses adresses. If k=1 was used all the time, only the private keys of the dead address will be revealed. There is still no known way to steal your BTC in this scenario. So the RFC6979 is good to have, but you are safe even without it.
Please correct me if I'm wrong.
I think you're wrong: the idea could be for the trezor devs to use k = in order to leak the seeds of people to the blockchain, visible only to them, of course.
It's a potential attack by the trezor devs, not just anyone.
There are million of ways how wallet devs (including trezor devs) can leak your seed. Some quick ideas:
1. Use above when the amount is above 10BTC (you don't care about poor guys anyway).
2. Use only last 16bits of RFC6979 and xor this with seed. This way k is still deterministic, but easy to break.
3. Leak the seed in 1000th transaction (or milionth...)
4. Leak the seed with some particular transaction. I.e. if the amount mod 97 is 32, leak the seed.
5. Leak the seed with the special, undocumented command in the interface.
6. Combine some of above or invent your own.
In my opinion, the true random k is a better option than RFC6979, but some devs don't even know how to generate random numbers and they still write wallets to store your money....