To the extent a radiant barrier works in an attic, it must face empty space towards the underside of the roof. Hanging it below ocspf is pointless. The "energy guy" is right.

Here is a link that might be useful: US Dept of Energy on radiant barriers

Yes agreed.

Radiant barriers are generally only cost effective in hot climate (possibly mixed climate) with traditional vented roofs.

Open cell spray foam on roof deck (other side of roof structrual sheathing) would mean unvented roof thus not compatible with radiant barrier.

Now if you sprayed the OC foam to drywall ceiling plane and kept vented attic it might still make sense but probably not likely depending on if you sprayed to code minimum levels. If you spray to code minimums and stick to best practices of keeping ducts out of that space then absolutely dont waste money or effort on radiant barrier.