These guy who say they get 20-50 firings because they are neck sizing only are full of s**t!!
*Not neccessarily. Some of us 'ol curmudgion's ... are only the 1/2 fullashyte

. There are ways to make brass last almost indefinately.*
Regardless of whether you FL size, or neck size, cases fail most frequently due to cracks in the neck, not elsewhere.
[this assumes you are setting up your FL die properly]
*Agreed. The occasional anneal reverses work hardening of the case neck.
Also improves accuracy, as neck tension becomes even again.
Haven't split a single neck since Turdo Sr. flipped the bird.*
Since the neck is worked equally, whether you neck size or FL size, there is very little difference in the life of the brass.
*Not so. Common FL sizers over resize the neck, then drag the expander button back through to establish a tight grip for the seated bullet ... too tight in some cases. Not unusual to see the neck OD reduced by .010" or more, than it needed to be. Every pass through the die.
Contrast this to Lee Collet or a bushing neck sizer that moves the neck only once, and typically only enough to achieve 2 or 3 thou. of neck tension.*
However, there are exceptions....for example, many Lee-Enfield rifles have such generous chambers that FL sizing works the case very hard near it's head, reducing case life dramatically.
*Agreed. However, I have LE .303 cases that have been fired so often I've lost count .. over 15 for sure. First firing is with long cast bullets jammed into the throat, or, that crafty 'O' ring trick. No case stretch happens in front of the web. Subsequent reloads by collet neck size. Occasional anneal, and/or a partial Fl shoulder bump if the bolt handle gets a wee bit stiff.*
Neck sizing helps mitigate this issue in the Lee-Enfield and other military rifles with generous chambers.
Personally, I do neck size some rounds that I use for competition.
For hunting, I FL size all my hunting loads to assure they will chamber easily.
Regards, Eagleye