We used to sell them. At one point the Heatline Capriz and Glowworm Betacom were identical, and I think that the Heatline factory still makes some entry level stuff for Glowworm.
They are made by DemirDokum, a turkish subsidiary of Vaillant gmbh (the parent of Vaillant UK).
They have made lots of models over the years that varied from "well, what do you expect at that price" up to "hey, thats really quite a nice boiler!"
We dropped them when they changed their technical number to a premium rate "09" number, as we thought it was incompatible with our "trade" policy, and made it clear that the brand was targetting a sector of the market with which we didn't want to be associated.
However, DemirDokum are a sound manufacturer -the Heatline radiator is excellent. But as the UK official importer of the radiator, I would say that, wouldn't I?