I really don't find the GW-M hard to read during the day; albeit that's it not as contrasted, clearly, as a positive display. its a bit worth in low light/dusk but you can turn on the auto EL if that bothers you - I don't find I need it either way.
I would go with the GW-M5600BC just because you have the solar functionality which allows you to use the EL as much as you want. And considering that these reverse displays can be difficult to read in different lighting situations, you may be using the EL a lot. If the contrast doesn't bother you, however, you mind as well go for the cheaper alternative, but keep in mind that it doesn't come with a nifty composite bracelet.
A forum community dedicated to watch owners and enthusiasts. Come join the discussion about watch collections, displays, watch winders, accessories, classifieds, and more! We welcome all manufacturers including Casio G-Shock, OMEGA, Rolex, Breitling, Rolex and Tudor, Seiko, Grand Seiko and others.