Please don't tell me about how I need a professional to be doing this. I'm simply trying to figure out if I should have someone do option A or option B.

I had my basement professionally spray foamed with closed cell spray foam. I want to get some HVAC air returns installed in the walls before I drywall them.

My question is, Should I get the air returns enclosed in metal or just drywall over and leave the cavity as the HVAC run inside the wall? I've had a couple HVAC'ers come by and say there's no need to install metal HVAC runs down the wall cavity and their pricing still seems steep! I'm just wondering if they just want to do a wham-bam-thank-you-mam job, or if there really isn't any reason to include metal in the vertical return runs to the HVAC system.

Any pro's or con's?

Much appreciated