One thing about side l9cks is their tendency to be weaker in the wrist area than box locks, due to the amount of wood that is removed .
L.C. Smiths can be particularly troublesome that way.
However, sidelocks are still very popular omong some shooters. Even though they are not as advanced a system compared to a box lock.
I do find side locks easier to clean and tune than box locks however.
Side plated box locks are nice, but no better than a normal box lock , of course.
The best thing about a side lock? Easier to put the hammers on it than a box lock! LOL
That is just my opinion however ......
Cat