I've been shooting the 7mmRM for about 15 yrs and I have never had a problem with that bulge appearing above the belt. I'm not saying it doesn 't happen, just hasn't happened to me.
Several years back I was fortunate enough to purchase 500 virgin Remington brass for $20.00 at a gun show. The first thing I did was FL resize them all, as I loaded/needed them. I kept them segregated as I shot them. On the next two loadings I only necked sized, some were a tight fit but I shot them anyway. I started over on that brass for a 4th loading (FL resizing again) but traded out rifles. I probably loaded at the higher end (hot) most of the time. That first barrel went south, the brass? they are still sitting in my closet (smoking, lol)!
No split necks, bulged or separated bases that I've seen from that lot. I saw the IT collet when it first came on the market and thought "I had to have it". I tried my best to talk myself into needing it, but I never could. I measured alot of my brass before and after resizing and decided the die was doing a sufficient job.
Do you "need" the collet? That's your call. I didn't then and don't now. JohnnyK.
"The pleasure you get from life is equal to the attitude you put into it."