I'm using 2 of them,(push-pull fan setup) and they work well. I just did'nt have the time to make my own. The shrouds keep the air flow directly on the radiator. I can't tell you they dropped my temps by X amount of degrees because I made a few other changes when I installed them....
I'm using the shroud/radiator combo on my P3 1.26S system and they are very nice. It will handle the heat load of that 1.26S running at 1711 mhz @1.81 volts, plus a 120 watt pelt with no problem, using a 103 cfm Sunon fan. I figure that it is dissipating around 180 watts of heat with no problems and with my reservoir tank temp of around 35-36° C, which is where my waterblock returns the water to first. I'm about to add a 172 watt pelt to the system because I lost my 120 watt pelt due to AS2 foiling and becoming a conductor, shorting out the leads. I will see how it will do with an extra 50 watts of heat load in the next few days.
I just go 2 of them, and I think they rock! The only thing that I would change is to use regular nuts instead of wing nuts so I can fit my fans down on the screws, there is a protruding place from the fan, that blocks the wing nut from turning, nothing a trip to Lowes can't fix. The shrouds have a seal around them, and are light as a feather. The screws can fit through the fins without a problem, and can fit through 2 shrouds on the radiator. The only thing I have to do now, is straighten them up a bit, and get some regular nuts to secure my fans to the shroud. Good job dtek.
I bought 2 shoruds, and I am going to run them in a push pull configuration. I am not sure if the shrouds are already mounted, but they are easy to put on. I am using my own ford escort heater core modified by myself.