Where I encounter the possibility of "leg suck" is if I'm going too fast (usually on a downgrade) and I'm not in a gear where pedaling is applying force to the drive wheel. One who has ridden a multi-speed bike has encountered this phenomenon. Frantically trying to pedal and engage the drive wheel is fruitless and can easily create the condition where your feet disengage and fall from the pedals.
You are left with two choices. One, just coast until you feel resistance when pedaling. Two, gently pedal (you always pedal when shifting) and begin shifting to a higher gear until you experience resistance.
Okay, three, apply the brakes until you slow down and re-engage the drive wheel. Road conditions may be such that you just want to coast until you're back in control and that works for me. Also, I gently pedal and shift to a lower gear if I see that it will be necessary such as when coming to a stop sign/light or approaching another upgrade (and my tongue will be hanging out again ;-).
It's important for you to maintain an awareness of road conditions. As in defensive driving, think ahead to know what you need to do. I'm thinking that having your feet fall from the pedals could be due, in part, to inattention or panic. Of course, other factors may be present such as leg strength (or other physical conditions), in which case heel slings are recommended (safety is very important). Do what you feel needs to be done.
I personally don't see a need for clip-on pedals unless I become a "Trike Warrior" bent on taking long distance trips or competing in a serious competition. At 67 I just don't see that happening. The standard pedals have nice protruding cleats that help to keep your foot securely on the pedals. I would caution against smooth/hard/slick soled shoes because there is nothing for the cleats to engage. In fact, I would recommend thicker, heavier, stronger shoes that would protect your feet. I use walking/running shoes with a deep tread.
I cringe when I see people riding with thin, flimsy house slippers or flip flops. Riding a trike is fun, that is, serious fun and your personal safety is very, very important. Just like bicycling, a helmet is important as well. Schwinn makes an adult hybrid helmet with a magnetic type clasp if you have trouble with those strong, squeeze type clasps.
Gloves ensure better control of your trike. In warmer weather fingerless gloves are good. For colder weather I wear a relatively inexpensive pair of work gloves that are warm, but not too heavy and stiff. Check your local discount/farm/hardware store.
Very importantly, I always wear my RoadID
bracelet because my medical conditions, and other personal information, are readily available to first responders. I might not be able to speak, but my RoadID will speak for me. Since I don't carry a wallet I keep a five dollar bill in my shoe just in case I need a Dr. Pepper fix along the way. So far I've been able to resist, but you never know.
Those are my thoughts for the moment. Please join in, post, and help make riding your trike a safer and happier experience for all. Oh yes, these thoughts are my personal opinions based on experience and common sense. You are responsible for you own safety. I'm not responsible for your actions or inactions... 73 Hal