My apology for responding rather late to all the helpful comments (had to go through a couple of implants, a fill, a crown and a tooth extraction in the last few days, lol). Thank you to all for your responses.
The top priorities in what I'm looking for in a monopod and a head are:
1) Overall gear weight (am getting old with some health issues, so the least amount of weight is of utmost importance to me now).
I thought about Jake's mention of Sidekick, but while I love the idea, I really don't want any additional weight if I can avoid it. I'm assuming the set up is heavier? The same concern with Sirui SUP204SR Photo/Video Monopod. While looks wonderful and I could achieve a Gimbal like function with it, it's a pound more than the Gitzo monopod.
2) The monopod/head combo is mostly for my bird photography (portraiture and BIF), and I need solid reliability in being able to carry over my shoulder.
I did closely read the reviews on Sirui L-10, but the following comment by one particular reviewer steered me away to the consideration of Sirui L-20S in spite of knowing that I don't need a panning feature (except that I could use the feature on my tripod for landscape, so the feature is not useless to me): "This rating (4 on Amazon) is based on testing this tilt head w/ a 200-500mm lens; I felt I had to over tighten the knob to keep the lens from tilting and this primarily happened while resting the monopod on my shoulder, but not exclusively." I might end up with the same issue with the L-20S, but considering that it's load capacity is 55.12lbs in comparison to L-10's load capacity of 33 lbs, I'm hoping that the issue is non-existent.
3) As a couple of you've already pointed out, I need to be able to go from monopod attachment to handheld in a hurry. I don't know how quickly I'll be able to accomplish this with L-20S in comparison to the lever action, but if there's a "significant" difference, enough to lose a chance at a good shot, then I'm willing to pay a lot more for RRS MH-01 Pro.
I guess the only way to find out the overall weight, feel, reliability, and how quickly I can detach for handheld action with the L-20S is to give it a try (including on my tripod for landscape panning). If there's anything concerning me with it, then it's going back and I'll order MH-01.
Should I go with the MH-01 Pro with lever, does anyone have a recommendation as to which camera plate I should get for it?