I don't currently use a collet neck sizing die for any of my cartridges, but everything I've read about them, puts them in a class above all other sizing dies. According to one manufacturer of a collet die, brass life will be extended almost double that of a conventional neck sizing die. Now I don't know how that number will equate with my personal reloading style, considering I load for maximum obtainable velocity, and am constantly pushing pressures to the absolute maximum, but I don't honestly think double is a realistic estimate for my loading style. Currently I manage to get about 12 -15 loads from my 7mm RM brass depending on the head stamp. To increase that to even 15-20 cycles would be well worth the investment, but to think I could possibly see 25-30 loads from my brass seems unrealistic. But having heard some rather reliable claims that brass life spans are as high as 30 plus reloadings, makes it a plausable possibility.
Regarding accuracy, if the collet die isn't going to take away from the concept of what a neck die accomplishes for me, which I feel is unlikely, it should be a rather worthy investment. If I were you, having not already purchased the set up I currently use, I would certainly buy the Lee collet die.