Plate heat exchangers block alot on the ch side, but also (area and water quality dependant) block from scale build up on the mains side.
Typically the supplies for Boilers (filling loop thereafter) are piped bypassing any ion exchange type water softeners due to aluminium heat exchangers rotting through and leaking through the use of softened water.
So the intergas approach is perfect for those in hard water areas where a water softener is installed as the supply to the boiler (including filling loop) can be fitted with no concerns about the water coming into contact with the aluminium.
Stainless heat exchanger obviously avoids this problem too, which there are plenty to choose from (at least in combi range... Seems to be quite a few less on heat only for some odd reason).
If you've got a knowledgeable installer who is very familiar with intergas and the use of opentherm with it then I think it's a great option personally.
Baxi 600 combi range is also good and value for money (brass, stainless steel and copper being primary materials), the heat only range on the other hand isn't as good in my view. Wish they'd make the heat only range identical to the combi just with blanking plates on diverter valve and plate heat exchanger point like glowworm used.