I can relate to the question. If you're first time buying, it's really hard to make the decision. You get conflicting advice, yet clearly hear of the risk from those that made a mistake, or know of someone else who did. Top end sliders cost a bunch, weigh more, and therefore are far less likely to leave the truck so you can use it for something else. Manual sliders are not so bad for cost and weight, but then they are manual - and you have to remember to use them. With the Reese option off the table, you're left with "Spend money/weight for something that you might never need or take an expensive risk that you should have"
Yamerhammer indicated the best solution (which I didn't think of when I bought mine last year) - have the dealer demonstrate the backing with the 5th you're interested in, using a standard hitch, in a bed the same length as yours. Especially if you verify how your truck will vary in measurement from the demo truck, you should have a much better basis for deciding whether to buy a slider or not.
2012 Ford F-150 Eco, Max/Max
Jayco 26.5 RLS, Reese Sidewinder