Hi,
FWIW, I blew some 2SJ's & 2SK's I had in a regulated power supply about 5 years ago, and needed to replace them.
As the originals were no longer available, I got details of the Magnatecs and Semelabs equivalents from the respective makers, and the specifications were identical. I therefore spoke to one company (unfortunately I don't now recall whether it was Magnatec or Semelab) and I was told that they are identical parts, with the only difference being in the package markings, purely for marketing purposes.
I mention this, since, *at that time* there was a substantial difference in both the ready availability and (more importantly!) the prices of these Mosfets.
Incidentally, the reason I had used these Mosfets in the reg. PS was that I had earlier removed them from the outputs of an 'older' power amp, so I had them to hand for free. 🙂
I had replaced them following the discovery that some Toshiba To3P near equivalents 'sounded' considerably better than the Hitachi devices, which I had been faithfully using for many years.
It is interesting to learn from J-P that someone is now manufacturing the 'old' Hitachi devices again, but I think you can do better than these old types now, as far as the sound goes.
Regards,