A '3 car' CityLink Metro vehicle is no longer than a 2 car 150/2. Some services will therefore see no increase in capacity with no toilets and possibly no room for bikes, along a route which follows the popular Taff trail.
I was under the impression that they’d be coupling a lot of these together? Given 4 trains an hour between Merthyr, Aberdare, Treherbert and Cardiff, all of which will apparently take less than an hour, I can’t imagine they’d need much more than 12 to run (plus extras for contingency). Since they have 36, wouldn’t they have the capacity to run every single train as a 6 car?
(Admittedly, I’m not an expert on this at all, and I’m only here because I’m curious, so my numbers could be all wrong!)