I have a HK 430 Twin Transformer from 1976, I bought off from EBay in order to refurbish and use it. I changed the cheesy binding posts, recapped what needed to be replaced. I even had a hospital grade power off to replace the rather thin power cord that came with it.
It was used to drive a pair of Gershman Audio x-1 and Sw-1 tower speakers.. the original review stated that these speakers needed at the very minimum 100 watts high current amp designs to be driven properly.
The HK drove them like a champ without much issue… and we are talking about the specified output of 37-40 watts per channel.
The twin transformer design is not gimmick and while it might not have the refinement of later SS designs, I have noticed the typical Harman Voicing, warm on the upper midrange but in a pleasant way that does not obscure details.
It is a win.
Other amps I am familiar with: McCormack, H2O audio, Bakoon, Lejonklou, Tubed 300B, Tubed F2as, Audiosector, Naim.