Jadis JA30 Mk2, how great???

The SE300B is a different Jadis amp actually and it looks to be parallel single ended and not pushpull hence the lower wattage.
http://www.jadis-electronics.com/en/se300b-43.php

Got it. I'm not really a fan of 300B single ended amps. Not because I don't think they sound good, but more because they are so very limiting as to the speakers that you can match them to. Plus, I think in many cases the 300B tube is more susceptible to noise from microphonics. 
In that perspective, I much prefer an 845 ( which Jadis also makes).

Jadis is  one of those companies that just consistently has  the knack of  building beautiful sounding emotionally engaging amplifiers that connect the listener to the music. There's obviously something they understand  and are executing  right.  

I'm a 300b SET aficianodo through and through. I haven't the opportunity to hear the Jadis SET offerings but I'm confident that they got it right. I heard a Jadis el34 push pull integrated (Not even one of their higher level models)  and it was very good sounding.  It displayed that special ability to pull you deep into the music..

It they can achieve this level of sound quality with an el34, I can imagine what they're capable of with a 300b in their  upper level range of mono block amplifiers.  As daveyf noted you just need the appropriate speaker matchfor the amplifier. 
Jadis is exceptionally adept at reproducing music beautifully. 
Charles 

Indeed, Jadis does make beautiful sounding and emotionally engaging amplifiers. To that, I think their build quality is basically second to none.
IMO, if one is looking for a tube based amp, then these need to be on anyone's short list.

Thanks all for your comments! I have just found how good the JA30 sounds, so arouse me of much interest to get their 300B amp as well. But honestly it seems can't bring enough power for my Sony AR1 speaker which was also newly bought! Anyway I will run them well for the next couple of months to see how changes they will be!