I've been in a couple of homes that have this retrofit and both had the
tubes suspended in the joist bay, not stapled directly to the subfloor.
Apparently, if you insulate well, it's not that much more inefficient than
the aluminum plates stapled to the subfloor.

I think it is significantly worse, but I could be wrong

I've heard from many that this methods is noisy as the plates
expand/contract.

glue is the answer. The pex expands in the alum, but if it is rtv or
urethaned in, it can't
If you ever add hardwood flooring, nails can penetrate the PEX tubing during
install.
Hanging them 1" down the joist helps alleviate this possible problem.


If they are in plates, you know where they are. My above the subfloor
system had no punctures.....til this year, under the floor where it
exited, caught it before sheetrock went up, so same could happen in any
system. If you ever add hardwood[is this really oging to happen?], you
trace the[ perfectly straight] path of the tube in plates, and avoid
them, usually running at a right angle to the tube helps.