The Jet Funnel mag well is used to aid in quick mag changes and was originally made for the USP Expert. It makes it easier to get the mag into the gun because this upgrade creates a flared opening at the bottom of the grip. This makes the mag well entrance wider and in turn a much smaller chance of missing the mag. well during fast or stressful reloads.
The Jet Funnel is currently made for 9mm and .40 caliber USP fullsize pistols only, although some people have modified theres for use with USP compacts. Also, the addtion of the Jet Funnel requires the use of higher capacity magazines. Capacity on the 9mm goes from 15rnds. to 18rnds and the .40 goes from 13rnds. to 16rnds.. These are necessary because the mag. must be long enough to reach into the chamber, standard mags are not long enough to work with the JF.
My Combat Competition USP .40 has one and it comes standard on this pistol. I assume this would be very useful for tactical shooting courses, but when shooting at the range there really is no advantage simply because you are not in any hurry. I have never tried it, but I think there would be next to no chance of the JF fitting on the P30 due to the very different grip proportions in relation to the USPf.