that question is whats the difference between a motorized fish finder/sonar (analog flasher) versus a digital fish finder/sonar. digital draws a much finer line than analog finders. you get more options to tune digital with over analog. there is no lag on the lx digital s.
of the two you asked about, the lx-5 motors fail a lot and i would not buy one for that reason and because its old analog technology.
the digital will show more by far because the line is so much smaller and not a fat line. on the other hand a marcum troller is only a 2" target separation versus the lx-7 at 1/2" target separation. that means the troller line will be thicker than the lx-7 by far or should. i have not used one to verify.
so if you are shopping look at target separation (smaller is better) and if its analog or digital.
i have a analog sonar too. the humminbird ice-55 and it has thicker lines and not as many features and flashes in your face to show the lines (thus the name flashers) and is some what annoying. you can not change the display to show different charts like the lx-6, 7 and 9 does. what you see is what you get with analog. you get flashing thick lines that represent your jig, then if you have zoom, then its all amplified or magnified.
my lx-7 failed after 6 times out because of a ribbon/data cable fell off of the face plates control panel. easy fix and should not have happened. sounds like they forgot to add a locking mechanism to the connector. a dot of hot glue or epoxy would stop it from happening again. other than that problem they are not breaking down.
its nice to have the best of both worlds to compare like i have been. the analog sits in the back of the bus for now and only comes out for the wife or as a back up like it was once already.
