I would suggest you ask an architect what their opinion is on these types of systems. I haven't seen any scientific research on them and how effective they are.
Honestly most architects don't have a clue about mechanical systems (ie ventilation, heating etc). Generally what the care about is what the wall controllers and the diffusers look like - not how or why they do or don't work.
That is a sweeping statement. If you get a good experience one who knows their stuff, they will know a lot about ventialltion and the best options. I well designed house can hve natural ventialltion using the 'stack effect' and passive solor heating and cooling, which can do away with the need for such ventialltion systems anyway. These ventilation systems that you install are generally a sticking plaster solution for poorly designed and insulated houses, which make up the bulk of NZs housing stick.
I don't install them, I don't sell them. I work in the industry and have a pretty good knowledge of how they work.
My statement is based around experience of dealing with architects who don't know what they are talking about with regards to these systems. It's not what they do - it's mechanical services engineers who are trained to design mechanical systems. Some architects have knowledge of mechanical systems but if you want to talk to an expert talk to an expert - a mechanical services engineer not an architect.
My parents do have one of these sorts of systems installed about 15 years ago, although not the brand being discussed here.. One thing that does concern me about the ones that suck air from the roof space, is that just below the input fan are fibre glass batts. These glass particles in the batts are tiny, and I would doubt the filter, which just appears to be a white fibre sheet, would stop these particles from getting sucked through it and into the rooms.