are there any safety requirements? ionization, etc...
from this list, which do you like
https://www.amazon.com/s/ref=sr_st_revi ... eview-rank

None of them, actually. There should be NO oil diffusing around birds because it's dangerous - see my article at http://www.littlefeatheredbuddies.com/i ... erapy.html

Ionizers shouldn't be used around birds either. The best air purifier to use around birds is true-HEPA. You'll need to change the filter sometimes, but it's safe and very effective at removing particles from the air. Nowadays a lot of air purifiers have several features built in, so if it comes with an ionizer make sure that the ionizer can be turned off. And if it comes with an oil diffuser, don't use it!

Carolyn, thank you very much!
If you have a link readily available, plz share.

For example, the very first one - I don't see anything about oil diffusion, HEPA filter is mentioned

https://www.amazon.com/IREALIST-Desktop ... r+purifier

Yes, something like that would be good. One thing to watch out for with air purifiers is that some of them are a lot noisier than others. So read the reviews to see what people like about a particular model and also what they don't like. If you see a lot of people complaining that it's noisy then that's a good one to avoid. I bought an air purifier once that had excellent reviews for its effectiveness, but it was so noisy that I couldn't sleep - and I can sleep through almost anything! So I returned it and bought one that was quieter. They're all going to make some noise, but it doesn't have to sound like you're directly below the flight path to a busy airport.

Also look at how big of an area they cover - they should all provide information about the square footage that they're meant for. Smaller purifiers might just be good for one room, while bigger ones can cover several rooms. Cockatiels produce a LOT of dust, so a more powerful model is good to have, even if you only need it for a small room.

thank you, thank you!