Pathos Inpol tubes

I know there are'nt too many Inpols around, though they are a wonderful amp. 50watts Class A, Hybrid integrated. I just wondered if anyone had tried different tubes. It's just that I saw the review of Shuangung Treasure 12AU7 and 12AX7 tubes from Grant Fidelity on positive feedback, that looked promising.
In fact, an opinion on the tubes used in any application, would be helpful, thanks