Frame Stiffeners-Good or Bad?

[JDon99]

I'm building my 66 shortbed for street/strip duty. I'll be running a narrowed 9 inch and wider tires. Powerplant will be either a healthy LSA setup or a 370 ci/80mm turbo. I had purchased a Tinworks Fabrications frame stiffener and trailing arms for the truck. I've seen some say the stiffeners aren't a good idea and are hard on the frame. I'd like to hear other's opinions or experience with something like this. I won't be caging this truck.