So, to update and thank everyone for the input
I went with the M324s, which came with multi-directional cleats. I installed them Sunday (with great help from BF Mechanic's forum).
The inaugural ride was yesterday, and I must say I'm pleased. I started with the flat side up and riding the path out to the driveway, then to the street. Right out of the box, I noticed the flat side was grippier than the OEM pedals, enabling you to put force on the pedals in a larger arc. After stopping at the street, I realized one pedal must've turned to the clip side and decided to just keep riding and flip it at the stoplight. As the light was green, I made my right turn and started climbing. The lumpy feeling in the one pedal went away, and I realized suddenly that I was clipped in on that side, lol. I had a second of panic, then just turned my heel out and unclipped. The plan had been to go to the park, and and practice on the grass or paths. Thought to myself "oh, what the hell' and clipped that side back in. I had a 3 mile climb with a couple of stoplights and practiced clipping and unclipping as I rode.
My phone app has a feature that verbally updates your progress, and it started saying I was "ahead of my previous record". I looked down and realized I been climbing one and two gears higher with just one clip in! When I got to my first level street, I just went for it and clipped both sides in. I finished the whole 12 miles that way!
Impressions- on the loosest setting, they stay engaged, but a twist in either direction (or even a yank up) will easily disengage. The psychological fear of being trapped dissipated almost instantly and I can see how they might make you feel a little more secure- like a seatbelt.
I'm definitely faster climbing and more confident downhill, as my feet stay attached to the pedals. It
is the efficiency- and I used some new muscles.
After I'm really comfortable I'll adjust them a bit. I'm a little awkward engaging the clips, and flipping them over is a bit slow, but that will all improve with practice.
Thanks for all the help and encouragement!