saw a cross over kit for 454/502 efi motors that replaces the circulating pump and gives 15-20 hp ? what are the pro's and cons of this unit ?

I'd like to see someone prove out the claim about the 15-20 horsepower on a dyno. Personally I don't believe it, and I figure Mercury Marine has done extensive R&D on all the possible ways to wring all the horsepower out of the engines as they can and still retain reliability. But hey, what do I know? I run wood through a machine for a living.

i think with crossovers as on my 502's they run too cold and that is not good so we are pulling em off and going with the stock hp set up,,
if have big blower motors that make a ton of heat i think crossovers would make sense, and yes i agree with crazy horse as merc has put a couple bucks into figuring out what would be the best set up,,
my o2
not a mechanic i am a pencil pusher,, so what do i know?

I installed a crossover on my 7.4 MPI a couple months ago. My circulating pump was leaking, so I just figured I would replace it with a crossover and not have to worry about it again.
I too, would love to see some proof as to the horsepower gains. I did not notice any difference after installing my crossover. It still runs the same temp, no gain in performance at all.
I did notice that my water pump was no longer leaking!!!
The crossover for the MPI engines don`t come too cheap either! They have the pulley attached so that you can retain the serpentine belt.
The whole kit, crossover, fittings, thermostat and housing and all related hoses, clamps and gaskets set me back $499 plus shipping (from CP Performance).
It sure looks purty though!