I carry mine tip up. I like to grab the knife sometimes placing my index finger under the end of the pocket clip to remove the knife. Then I turn the knife to position it to use my thumb to open the blade with absolutely no flick of the wrist. IMO, there is only one reason to do any kind of wrist flick. That would be to open a knife one-handed that has some sort of resistance to pivoting. The pivot may be too tight or maybe a little corroded. I see videos of people opening knives with a wrist flick but close them by releasing the lock and letting the blade fall. The falling blade means the pivot is working perfectly or too loose if anything. Using a flick to open a knife looks cheap to me. That sounds much worse than I really mean. I mean cheap knife, not person. Flicking a knife open puts the mental picture of a 1950s gang member flicking his knife open (usually using his entire arm) in my mind. I know that is narrow minded.
I got a look from a cashier once when opening my knife at a cash register that I really enjoyed. I needed to open a package and with a normal speed movement, removed the knife and opened it drawing no more attention to my hand movement than doing anything else. The package was in my left hand and I had an open knife cutting it open that seemed to appear from nowhere. Not because of speed but because the deployment was as natural a movement as removing and opening my wallet. The look on the face of the cashier was as if to say "where did that knife come from?” I think I read the expression right. I wasn't trying to be fast but it was fast because since "getting into" knives I play with them a lot whether it be trying to get used to deploying the thing or just playing with them while doing things like watching tv, walking dog, or having sex. Repetition increases speed without you even knowing it.
So, I pull the knife out, turn it enough to get my thumb in the hole and push the blade open keeping contact with the blade until it locks. I think speed is something that is almost never needed. I mean the "quick-draw" speed of a gunfighter. Even in a self-defense situation you probably only need the lightning speed if you are up against a martial artist of high skill. If I’m up against that guy speed is very important. I run fast.
I really got long winded and I'm sorry. Evidently this wrist flick issue is something I need to seek counseling about.
My final answer to the flick thing is, if you need to flick, flick. If you don't need to flick, flick or don't, it's up to you. If you like the popping sound (I do) of a knife opening then do it.