Nice find! This looks promising.
I think a 6J1 is a pre-amp tube and a 6P1 a power tube. I've never heard them but have read that they're pretty cheap (hense the lack of a roll cage), so upgrading the tubes after purchase would probably be wise. Good tubes will last for many hundreds of hours before needing replacement - I've got a dozen or so zenith and raytheon tubes still working fine in vintage AM radios after 30 years of casual use (although I burn through 6L6's in my guitar amp like you can't imagine).
Considering the amp is only 2.5W per channel, I wouldn't worry about heat.