They can be helpful if you don't have a ton of outside air coming in

I use a Dyson purifier and... it's been okay I guess. It helped a little bit, but whether it's worth it or not is debatable.

A couple of cons:

- You need to run it all the time, because otherwise it can take ages to filter out pollutants, by which time your allergies can get triggered.
- It works best if your doors and windows are always closed. Naturally, that won't make for a very healthy or pleasant home, so you might want to restrict the purifier to a specific room which has its windows and doors closed all the time. But then if you consider air draughts, the pollen's gonna make it's way in anyways, so a strategic placement of the purifier is crucial.
- Obviously it won't help if you go outside.

So you could get one if you really want to, but don't get it specifically for combating hayfever. The one I've got also purifies VOCs (ie volatile organic compounds like formaldehyde, which can released by paint, carpets, furniture etc), and it also doubles up as a space heater, air cooler (fan) and temperature/humidity monitor. I've also noticed a significant reduction of dust in my room, which means a lot less dusting/cleaning needed for all the surfaces and electronics etc in your room. I can also control the purifier from my phone and Home Assistant. So it's nice to have when you consider all of those.

I have friends across the ditch who swear by Haytox - a medication which is administered nasally, it takes only a few minutes and you're allergy free for a whole year. Maybe get your partner to talk to their GP and see if it's available here? I haven't seen any mentions of it in NZ but maybe they've got something similar.