My understanding (based on my not so great memory of an EPA air filter report) is that there are two basic types of this general type of filter and the electrostatic ones do best near the beginning and get worse over time while the others get better over time but with flow rate suffering. There are a few consumer air filter makers that do much better than most of them, particularly when it comes to the smallest particles, and I think they rarely if ever use the electrostatic ones for the inner filter. Those filters also cost quite a bit; I think the electrostatic ones can do a better job at low cost. For smoke in particular filters can easily aquire a smoke smell that makes them unusable well before they otherwise would be, unless there is a large carbon filter before it, so that favors low cost filters.