Very good sounding, useful plugin (at least for me). Generally works with all audio sources or instruments, but I mainly use it as an additional gain and tone shaping stage in combination with electric guitars and (vintage) amp simulations.
You don not really get the huge amount of gain of a typical guitar tube amplifier preamp, but you get very convincing, authentically sounding, clean to slightly crunched tube tones, which work fine as additional tube booster in front of eg. an already good sounding Tweed, Vox or Plexi simulation. Bass also sounds great through this plugin, alone, but also in combination with eg. an Ampeg simulation the tone really improves - for my taste.
For more overdriven tones you can also cascade two or more of these units, which also seems to work very well.
Mixing triode and pentode character allows good control over even and odd harmonics. The tube simulations really sound - and also as important – behave and react very authentically to the input signal, in terms of attack and dynamics, which is not always taken for granted if compared to some other tube simulation plugins, I know. Here you get very tube typical tones and behavior and a very realistic harmonics reproduction.
Bass cut, circuit temperature and circuit power control allow good fine adjustment, as well as the three different, selectable tube types.
For me one of the most realistic sounding and reacting tube circuit simulations, I know. Good tones at a low, fair price, if compared with some other, similar products from competitors, which sonically did not convince me more, to be honest.
Nevertheless my personal wishes for maybe a future upgrade would be an additional treble cut, a mid-notch or even boost/cut with adjustable or some selectable frequencies between 250Hz and 2500Hz and also more gain or an additional gain boost option or alternatively a second, swichable triode stage.