Could this be used in a kayak?
No, This device is meant to be used in a chair/couch that is sitting flat on the ground. It is not designed to be used in/near water. Thank you for asking.
Can this device be used safely on a chair without arms, such as a dining table chair?
I used it on chairs with arms only, because of my balance problems. I think it can be used but depends on your situation.
What is the difference between the regular and premium model?
The main difference between the two is weight capacity. The standard model has a 230 lb. weight capacity whereas the premium as a 350 lb. weight capacity.
Can the device be placed on a cushioned chair seat, or should it only be used on a hard surface?
Yes this device can be placed on soft and hard surfaces.
What is the minimum weight a person needs to be to be able to use this?
It's adjustable to work for all weights up to 230 lbs.