This is a Russian made version of the Fender Groove Tube. The categorization for this item is wrong, it's a tube, not an amplifier. Fender's groove tubes are a varied bunch, in that their different tubes will work better in different amps. This particular tube tends to come in their smaller amps, ones that are typically used for practicing by oneself or with small ensembles. They tend not be the same as the ones that are in the larger amps, and thus, you probably wouldn't want to put these in an amp that has such a loud dynamic range and power, if you did it would probably be a waste because you wouldn't get the sound that you expect and you might blow them out.
While I tend to love Fender amps, I don't know if these tubes are necessarily the best. Granted, the tone on the smaller, practice Fender amps doesn't really come close to the sound of a Twin or a Deluxe Reverb, but I think that they are generally ok. I just don't know if these particular tubes are the best bet, I have seen other brands make similar tubes, and have read that they are better. I would like to see these amps get something a little bit more aggressive and bright with their sound. If they could come just a bit closer to the Twin, I'd be more keen on purchasing a Fender amp for practicing. I haven't had the time to try out a bunch of different tubes in my practice amps though, and I know from (bad) experience that these don't really work well in anything but a practice amp.
If you need to replace these, maybe look into getting something else, there's a possibility that something with a sweeter tone might show up.