The message
from Andy Hall contains these words:

These are quite inexpensive and as well as operating a lot more
quietly than the traditional Portsmouth type, have a clean shut off.

The potential drawback is that where previously you may not have had any
resonance as the valve shuts, with a Torbeck type valve you sometimes
get a mighty slam as it closes. It's down to loose pipework, and isn't
really the fault of the valve, but it's often a ******* to track down
where it's loose.

--
Skipweasel
Pay no attention to that man behind the curtain.