I have heard it at Detlofs place, who is a member here as well.
Both the Lamb as well as the VTL cannot touch it. The Dartzeel I am not familiar with. The unit is absolutely quiet, even if wide open, highly resolving and very dynamic. It is neutral and in comparison to the other units mentioned has far better Prat at all sound levels.
Detlof drives the unit with NOS Mullards from the Fifties.
Hope this helps. If you want to know more, drop Detlof a line. He is a nice and helpful person.