I've got a few of the Klark Teknik tube EQs and compressors. Once you change the tubes in the signal path to something better (I used Tung Sol) they improve quite a bit (dirt and constricted dynamics go away). You need the right screwdrivers (Torx-T10 and T9) to open these units, BTW.
I don't believe there to be anything wrong with the audio transformers. An area of improvement would be the power supply filtering, I would prefer less residual hum. The switching supply will probably not live as long as a good linear one.
At the price these are being sold here, even with the tube upgrade, I couldn't DIY them and they are really good.