The one we have has a strap that goes around the box spring to keep it in place, it's very secure. I think it also would make a difference which kind of mattress you have, a 6" lightweight foam is not going to support it as well as a heavy 10 " coil.
My Dad had also used an under the bed type rail which he needed to help him sit up and stand. He was quite happy with that rail. But every week I did have to push the rail back toward the mattress as Dad would eventually work it away from the mattress.
Are you looking for someting to keep him from falling out of bed or as a grab handle to get in and out of bed? I used the under the bed type for my mom whose about 160 lbs and it works great as a grab rail for her. They are cheap and easy to install. It might work for a 195 lb man if he is still somewhat ambulatory and/or has assistance.
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