Ruike P108 is a quick opener for sure. I have one and it’s fast. The Ganzo’s are pretty fast too. Not as quick as the Ruike but, quick none the less and down right super affordable. My quickest manual flipper is the Sanrenmu 1161. It’s hands down the quickest and smoothest. Of course I can only compare them to other knives I’ve had so, I’m sure it has some stiff competition. I’ve just never had the chance to play with one.
It sounds strange but it holds true for both the Ruike and Sanrenmu. The harder you try to flip it open, the more difficult it becomes to succeed. Playing with it for just a few minutes will find it’s sweet spot for you but, I have a neighbor who couldn’t open it to save his life. My 11 year old son looks at it, picks it up and flips it open like he’s had it his whole life.
Amazon has the Sanrenmu for less than $35. Might be able to find it cheaper but you won’t be able to beat the delivery speed.