The use of 1 or 2 hands for a concealed draw-stroke is largely dependent on the garments being worn.
I spent about 13 years before retirement in a plainclothes assignment. It wasn't UC, but a suit/sport/casual coat type of assignment. That meant I did a lot of practice clearing my coat (or
coats, if a raincoat was also being worn) drawing 1-handed. During cooler weather, I also wore a fleece of jacket when working in my additional firearms instructor role (outside range), so it was an easy thing to do a lot of live-fire practice wearing that sort of cover garment when working range sessions.
Now, off-duty, in colder weather, I'd sometimes find myself wearing a sweater/sweatshirt under a jacket. That necessitated becoming familiar and comfortable using 2 hands for the accessing the belt holstered gun for the draw-stroke. The off-hand did the lift for one garment and the strong hand did the usual sweep, reach and grasp draw from under the other garment.
As with many things in life involving repetitive coordinated movements, it required a lot of successful properly executed repetitions in order to get things down to a smooth movement where I didn't have to stand there and think through the process step-by-step. It had to become reflexive if I was going to rely upon doing it while possibly having to do other things (crouch, step offline, lean back in a chair, twist away from something, etc).
Well, hey, do you think you might need to do it ... or you might desperately
need to do it right, and do it right the first time while you're trying to catch up with unexpected events?
This is the sort of thing where a good instructor can help acquire the combination of movements involved, especially someone who's done it for a long time (meaning some thousands of properly executed, smooth repetitions).
Do you have to stop and think your way through the process of unlacing your shoes, or just slipping off loafers? Does it make you stop and think if you're unlacing boot laces through eyelets or around hooks,versus just unzipping a side zipper or tugging off a Wellington boot? Or, have you done all of those things for so many repetitions that you automatically recognize which is needed, and how to do it without having to stop and consciously think about it?
Does removing your wallet from an open rear pocket, a velcro tabbed rear pocket or a buttoned rear pocket stymy you, or do you automatically adjust and accomplish it with relative ease and smoothness because you know what pants or shorts you're wearing, and what's required to remove that wallet without fumbling it and tossing it away from you?
If it's not a natural movement, what is it?
What do you want to be able to do in a high stress situation?