Just to chime in here,
Meguiar's Marine line is not the Professional line in blue bottles.
For example, the #50 Cleaner/Wax, while yes it is a cleaner/wax, is much more aggressive than the #6 Cleaner/Wax because Gel coat finishes usually require a more aggressive product because of the way they oxidize.
Most of the time when questions like these come up, it's easy think or say that the products are the same, but that is usually never the case. Similar, yes, exactly the same? no.
Take the Vinyl Cleaner Conditioners in the Pro line and the Marine line. These two products are very similar. There is only so much you can do to clean, condition and protect Vinyl.
The difference in these two products is in how they leave the surface after application. M-40 will be very slippery on vinyl if it gets wet, which can easily happen on a boat. Someone steps onto the seat to step out of a boat and Bam!, they end up on their head. The Marine version takes the abundant presence of water in the setting and leaves behind a surface that won't be as slippery if it gets wet.
Sometimes the differences are subtle, sometimes there dramatic.
Take M-6332 One Step Compound for example. If you use this on your car's finish, especially by machine, (rotary buffer), you will risk burning through the paint very quickly. It is a very, very fast cutting diminishing abrasive compound formulated specifically for Fiberglas gel-coats.
Hope this helps...
Mike