My Carrier furnace has the EZ flex filters (16x25x5). These come with the plastic end caps that fit on the expandable filters. Can a regular filter, non expandable, of the same dimensions be used as a replacement?
As long as the replacement fits without gaps (which would allow air to bypass the filter) will be "OK" to use.
Whether the replacement filter meets your needs (besides cost) depends on the effective size and screening size. It may be hard to compare these factors with discount filters
The effective size of a deeply pleated filter means you get a larger filter that will clean longer.
The screen size of the paper relates to how small a particle the filter removes. Its a tradeoff, because super fine filters (pollen level) will clog faster.