Heat recovery looks to be a better overall solution, but costs significantly more to purchase and install. The benefits of PIV seem to be you get a good chunk of the 'fresh air' benefits at a fraction of the cost.
Just to puit my 2p, while they do say that MVHR is not recommend for older properties that arn't to mordern air tighteness standards, and can see how this breaks the theory of the thing on paper in terms of energy savings etc. But I have an an older property that some of if is solid walls etc, the biggest place I used to get an issue through was windows, in winter you'd wake up and there would be enough water on the windows to leave a towel sodden after you'd wiped them all. Considered PIV as well as MVHR and went for MVHR and the window issue went away, and I have to open windows less which must be saving me energy over doing that (although not in the perfect way perfect airtightness and MVHR would on paper...)
Extra ventilation is required in rooms that make a lot of condensation suddently, like high flow shower in bathroom, MVHR cant be expected to coe with all though.
Lukily as its a bungalow and all the rooms requiring extraction where along the back of the property and all though requiring air inlet were at the front, it was not too difficult ducting wise.
Still need to sort the speed control, its running at its fastest speed with no set back at present, which is adding a little to the bills and is on the list to sort!