ALL Groove Tube tubes are basically someone else's tubes, that they test, and slap their logo on. 100% not worth the money.
And Groove Tube's pre-packed "specially tuned" triplets of tubes... what a scam. It's just a combo of either chinese, russian, or yugoslavian tubes in different orders. The SAME EXACT tubes that you can get anywhere else.
I'll pay someone else to test them. Doug from Doug's tubes, Mike from KCANOS, etc.
*****NOTE: for a while, GT WAS making an exclusive Mullar copy preamp tube, which was supposed to be amazing, but is now discontinued.