Both reusable and disposable furnace filter?
Given that more restriction actually lessens the load on a typical furnace blower (no, really, you can prove it with an ammeter - less mass of air moved means less work, and homeowners "opening things up to reduce the load" can actually increase the load to the point they burn out the motor) that's not a concern.

Essentially you have a prefilter (disposable) and what appears to be a washable electrostatic for the fine stuff that makes it past the prefilter. The prefilter keeps the dust bunnies out of the washable. Not sure why they would make the washable harder to access (annoying design philosophy) but yes, use both.