Wow, I didn't know that RPM Outlet was still in business.
Nothing wrong with the Zex product, although that kit is lacking a lot of things. I ran a 75 shot of nitrous on a Zex kit on my 2006 for 2 years with no problems. You need to adjust the tune for the nitrous, it isn't just hit and go. Also, I can't tell if that is a dry kit for sure, but it doesn't look like it has the fuel solenoid and doesn't have the nitrous management unit that Zex uses to combine the fuel and nitrous solenoids in one box. With the 2005+ Mustang you want a wet kit; it adds fuel as well as nitrous rather than relying on your computer to recognize the need to add fuel through the injector. Last thing you want is to run lean while spraying.
Make sure you have a nitrous pressure gauge. It performs best at about 900lbs but as you use it the pressure will drop. You also need a window switch. Even with Zex saying that the nitrous management unit (NMU) will learn when you are WOT and not fire before, it will mis-read. Before I had the window switch installed I was lining up to make a pass. Took the RPM up to about 2,000 to stage and the NMU decided that was WOT and fired off. Spraying too low in the RPM range is what will kill the engine. So got the window switch and set it to 2,400 rpm (window switch blocks the signal to the NMU until you reach the preset RPM and then it "opens the window" to the NMU).
It is nice to have a purge so that you have fresh nitrous ready to go when you are going to use it. And a heater for the bottle for those cool evenings and early spring or late fall trips to the track. DO NOT use a torch to heat the bottle. That will weaken the bottle and make it prone to rupture.
And Bschmidty is right. When the nitrous hits it adds a lot of torque all at once. The 7.5 rear end will break under the torque. Plus, with the open diff you will have problems getting the power to the ground.
Nitrous is really a track only power adder. You can't leave it turned on all the time or your solenoids will fail from the pressure. Many state laws won't let you leave it on anyway, some require you to disconnect the bottle until you get to the track. And at $4 a pound for nitrous it will get very expensive to fill the bottle if you are using it for daily driving. I could get about 10 passes on a bottle before it was difficult to keep the pressure up.