Maybe you don't need one at all. What do you want from it?

I bought one and while it certainly removes smells (at least it did while cartridges were new) I quickly discovered the obvious - it works only with windows closed and it takes a while before there is any effect. So it makes sense if you don't open windows (have climate system with filtered ventilation) otherwise you'll be undoing all positive effects in five minutes.

Also filtering cartridges are expensive AF.