I shot a box of it last weekend, and didn't notice any significant difference. The claimed velocity is no different than 17 grain, which makes me wonder about the propellant. The primary driver behind the 15.5 grain NTX, as far as I can see, is to have a non-toxic cartridge available to those who live in areas that have been hijacked by environmentalists, not to provide any new sort of HMR shooting experience.
I still prefer the Winchester Supreme 17 grain V-max.