I bought a few years stock (!) of filters from FairAir.Eu

They offered the option of G4+M5 (pollen filter) filters rather than the usual G4/G4 which I went for.

I fitted a set today and (somewhat obviously) the denser filter means you need to increase the fan speed to compensate. given mine is already a little high I don't want to do that.

So
1) a warning for anyone thinking of using higher filtration filters in their MVHRs. You'll need to adjust the unit if you set it up with something else
2) does anyone want to buy these at a good discount?

I bought a huge roll of the G4 filter stuff 10 years ago, and a ‘supaclips’ medium system. When the filter needs changing, remove the old filter from the frame, and clip new material on. Sure it takes 5mins, but you don’t need to keep buying as much stuff. Even the (stainless) clips are re-useable. VH plus sentinel kinetic.

Here's the external filter, probably been in for 4 months. It's all a bit filthy, I need a month of nagging before I change it.
The wire frame originally had a filter sewn onto it, but it seems fine to use the aftermarket clips in the pic instead, which is a lot easier. I think the pic shows the original frames, which are stainless steel - I did once buy a replacement filter set - it's almost identical, but gone a bit rusty.

I added in a secondary (or primary) filter box with a fairly coarse filter before the MVHR unit to get rid a lot of the 'dirt' before the air reached the unit filter. There is a thread somewhere on that as I had an issue with condensation on the metal box.