I have no problem with the "old" rings, I set them and forget them in separate turrets. They haven't loosened up yet. Some require channel locks to remove. The O ring is what holds them tight.
So much to do about lock nuts?
It depends on what equipment you load on, whether lock nuts effect your hobby big or little. Speaking of big or little, for an old thread a couple of years ago, I took the following picture:
Left to right top: Current RCBS with the brass set screw; really old RCBS for a uniflow; Forster split ring.
Left to right bottom: Hornady split ring, Old RCBS with ugh steel set screw; and Lee's with the "O" ring. (some people even drill Lee's out and add a set screw.)
I don't have a Dillon nut.....but they win the minimum size contest....but have no set screw or "O" ring.
All of these rings work for set once and leave it alone. Some not so well for when readjustments are necessary....as RealGun already pointed out.
For single stage, even the steel set screw and buggered threads work if you set once and never change it.......in that scenario the Lee works just as good until the rubber deteriorates, but you can't have a brain fart and loosen on the die barrel...you gotta touch only the nut. Their new split ring with screw version remove that gotcha for people like me who may forget it's a Lee nut under there.
For progressives it's another matter. The big round ones, including Hornady's with the sides flattened, can be hard to readjust on press. LnL bushings make it a little easier on the Hornady ones, but try to get channel lock on a populated die plate.....in fact the big Forster ring can't even be used on some, certainly not on my green 7-station progressive...stations are too close together.
For the Pro Chucker 7, RCBS rings barely work, better sized for it is the Lee, and even better the Dillon...but you can't repeat on the Dillon if you have reason to remove a die.....cleaning comes to mind.
So yes, lock nuts are a big deal for some of us.
Near as I could measure without disturbing the new dies is that the new nut is the same .300 (thickness) as the old nut. Diameter is 1.240 compared to 1.257 on the old nut at the corners. I would consider that insignificant.
Thankyou RealGun for measuring! I'm pleasantly surprised to hear that the new Lee rings are even smaller.....and that Lee gives you a choice to buy a split ring version......that and the little wrench that allows grabbing the nut from almost any direction of the compass is awesome. It just may become the ring I replace all my others with. Ordering a pack soon......