Bill, I have one and love it. When I was shopping for a hitch I had two things at the front of my mind: (1) a rail-free bed and (2) weight savings. For point 1, I use my truck as a truck - I am a vacationer and would be removing the hitch after almost every trip. I did not want rails getting in the way while sliding in plywood or sheetrock or while shoveling a load of top soil. For point 2, I have a pretty good payload at 2,949 lbs but with a further limitation of 2,500 lbs pin weight. Estimates for the 5th wheels we were looking at came in around 2,200 lbs pin weight. Keep in mind that the underbed gooseneck will weigh a little over 100 lbs but overall it still saves a good 100-150 lbs over most conventional rail-free hitches.
As far as hooking up goes, side to side is no different - just line up the ball with the hitch in your mirror. Backing up the right amount takes some time to get the ball in just the right place but after a year of use, 9 times out of 10 I can be within a couple of inches on the first try.
To be honest, there are 2 cons that I can think of:[list type=decimal]
[*]When you initially install it, you have to tighten the top nut to 50 lb-ft. Then you lower the 5th wheel down. Once the weight is on the hitch, you are supposed to climb back into the bed and re-tighten the nut to 50 lb-ft. This is a bit of a pain in the ass but I found that the nut will turn a turn or two so this is a necessary step. I did meet my first Andersen owner in person about 2 weeks ago who said the company just told him to tighten it to 100 lb-ft to start with but I cannot substantiate this claim.
[*]You have to raise and lower the 5th wheel more to clear the ball so it takes a little more time. But this is usually when I have my first cold one while setting up camp. 8)
[*]Yes, I know I said "two" but some may argue that lining up the ball front to back is a con since you might have to get out once or twice to get it right but I've talked to many users of conventional hitches (and watched them) get out and adjust the height once or twice so they hit the 5th wheel plate just right (yes, I know some have memory but I think that's a minority)
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I recommend the hitch without hesitation! The ride is smooth as can be and the hitch hangs on my garage wall when not in use. It has also started many a conversation in the campground from interested passers by.
Joe