Having used both my preference is for the direct venting type. The
condensing type produce quite a lot of (damp) heat in the room which
may be a good thing in winter but not so smart in summer.

That depends on the model. My previous one was a horrible Hoover, that did
raise the humidity. It would take many cycles to fill the container. The
Bosch could fill its huge container after drying one wash. And that was
after the clothes came out of a 1600 spin washing machine. There is no
noticeable increase in humidity when it is running, although the room does
get warmer. It is now plumbed in, so I don't have to empty the container.

What would be handy is a condenser that can use hot water from the CH.

The condensor would work best with cold water, not hot. I suppose you could
use it as a heat source on the CH, but this would fail as cost-benefit
analysis. You already get the advantage in that the room with the dryer
warms up, causing its TRV to turn off, saving on CH costs.

Christian.