Just turned 800 miles on mine and what I'm finding is that I really don't like the shift assist in the city and low speeds. (never get out of 2nd gear in town anyways). I find it to abrupt at low speeds in the lower gears. But when I'm on the freeway and want to go from 3rd to 4th or 4th to 5th I like it, and when I'm in the middle of nowhere and decide to go from 0 to something just short of losing my license fast, holy crap, it's a nice option then. And yes, it does feel " like being fired from a giant slingshot"!
Congrats on the bike.
I have the shift assist on my S1000RR and I am use it in the same way. I like my bike, but the K1300S is really nice....