The camper we have now came with FastGuns, which is my first experience with them. They are as the name indicates, fast. IMHO, any tie downs that are spring loaded as the FastGuns are, such as Happijacs, would be just as good while possibly not quite as fast. We used a version of Happijacs on the Caribou we had for 23 years and 200k miles without any problems. At that time Fastguns were not around or we may have opted for them.
I recently bought a set of used Happijacs to carry while we were looking for a camper in case the camper we bought didn't come with tie downs. I paid $50.00 for them.
I certainly agree with Jake though and would never use anything other than spring loaded tie downs, such as hardware store turnbuckles. A bit of give is necessary to compensate for the truck bed "twisting" on uneven ground as well as the dip Jake mentions. I always tightened the front tie downs until there was a slight pressure on the spring and left the rear tie downs a bit loose. Perhaps that was overcompensating for bed twist, but it worked for me.
IMHO, it depends on how much you want to spend, and how big of a hurry you are in when loading up, but spring loaded of some sort is the way to go.
1994 30' Monaco Dynasty, 5.9 230 HP Cummins, MD 3060, 1992 Geo Tracker.
1996 Dodge Cummins 2500 with 1996 Lance 945 camper