I'll be the first to admit that I got a bit carried away with this one. I love seemingly simple problems with constraints, because it usually means the design solutions are going to be fun.
Concept #1 is probably the most robust and consistent solution. It gets the job done, but is very similar to what already exist in the market. If I had to go with a solution with the least amount of worry, it would be this one. It's basically a threaded knob tightening solution, but the magic sauce is the spring that keeps the clamping arms always engaged. This was a common theme with nearly all of my designs, and it's what makes the one-handed attachment easy to achieve. Concept #7 is possibly my favorite because of it's uniqueness. Unfortunately, it has the most parts and would be the most expensive to make. It's also not clear how robust the clamping mechanism is. The inspiration from the design came from the ball and socket locking mechanisms for camera mounts. There is an upward pressure applied that locks something in place. I transferred this idea over to the bike handlebar mount. Again, a spring keeps a constant force on the clamp arms, allowing for that one-handed attachment, in this case turning a cam 180 degrees. The prototype is a tad tight and doesn't open up quite enough to clear the handlebars with ease. Since it's 3D printed plastic I'm able to force it with no issues, but it wouldn't be as forgiving if it was aluminum or steel. If I spent more time on it I'm confident I could tweak the design to get rid of this issue. (Spoiler: Concept 7 had the fastest time for attachment and removal).
Concept #13 is as seemingly simple as #1, and designs like this do already exist. Originally, the thing that made it unique was that the threaded shaft had a smooth section which was supposed to allow for a quicker attachment and removal. The thinking was, you would only need to engage 3-4 threads to safely lock the clamp. If you remove the majority of the threads you don't need, you can slide the knob out of the way to remove the clamp much faster. This actually didn't work when I tested it and it's something I should have caught in the design process. Originally I thought pushing on the knob would compress the spring even more, keeping the clamps held tight around the handlebar. In reality, pushing on the knob pushes on the first thread of the rod, which opens up the clamp. Huge design flaw. Looking past that, I actually don't think it buys you that much time anyways. Again, the spring provides a hold on the clamp for one-handed operation. (The 3D print I ended up with had a fully threaded rob, whereas the CAD and screenshots have the smooth section of rod).
Concept #1 Cut View
Concept #7 Cut View
Concept #13 Cut View
I honestly don't know how good my time-tests would be if I just had to guess based on sketches. My cheap 3D printer is on the fritz, but it got the job done and I came up with some times that I feel confident in. Your mileage may vary. I'm guessing Concept #7 will break at any moment.