radiant floor heat

i am going to install radiant heat under my subfloor for the first floor of our house. i am planning on using two runs of 1/2" pex per joist cavity with a reflective layer under it and 1" foam under that. most of our floors are hardwood or thin carpet. I have two real questions. first who makes the best zoning pumps? and do the metal plates holding the pex against the subfloor cause any problems i had a guy say that they cause discoloring of floors