A few days ago I was fishing for blue cod and thought I'd try a metal lure instead of soft plastics. Blue cod are super aggressive and destroy softbaits within seconds. I got myself an orange kabura style slider rig a while ago. After dropping that to the bottom I got hits right away and because it's a metal rig it can stand up to the destructive power of blue cod much better. I can now recommend those slider rigs for bottom fishing. They do seem to work pretty good and in the long run are cheaper to use than soft plastics - especially for aggressive toothy fish like blue cod.
It might be okay. There is not much strain on the back. Not much different from sitting in a chair and moving your legs. You could try in a gym on one of those recumbent bike exercise machines. Should be pretty much the same movement.
If you have a normal paddle kayak you have to use your back muscles a lot and move back and forth. But with the pedal kayak it's quite comfortable. I tend to get lower back aches easily. But haven't had any issues in this regard. Even after hours of pedaling around. If anything you get a bit strain in your knees after a while, especially in the beginning when your body isn't used to this movement.
It's an awesome fishing machine in my opinion. You have your hands free, don't have to buy fuel, can move back and forwards while having your rod in your hand for casting and jigging, hold position without anchoring, move around without getting tired too quickly and at the same time do some healthy exercise.