I have sidelocks which were old before I "WAS". They are still performing admirably, so much for the longevity part. I have never owned a gun with intercepting sears & have never had a situation arise where I felt the need for one.
I will admit though my favorite gun is a Box Lock, a Levefer Arms Co gun which in always resembles a sidelock except that the parts actually attch to the fraame. The parts essentially maintain the same positions as they would in a sidelock, they just don't attach to the side plate. It seems to take on the best attributes of both.
Incidently box locks date well back into the ML era, even to the flint age.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra