same as serge
Rads are stiffer, easier and faster to lace and unlace, (especially after adding a loop of material around the central laces to help pull them). when fully loosened the tongue hinges so far open that you can nearly touch the top of the tongue to the tip of the toe box of the boot.
i have tried the mareks in a store setting though... from memmory i would say the mareks did not open quite as wide as the RADs, but the system binding of course opens wider than anything out there, just got to get the boot on first. being able to put boots on without a board attached might be helpful to you, or maybe not?
the mareks have a little bit more defined heel kidneys and the marek boots themselves (without) the system binding are surprisingly soft and flexible, just a tad more stiff than the murrays. the RAD boots have a more rounded toe box and not quite as pointed as previous SS boots (some are liking this [i do] and some don't) the marrek felt tight across my foot where the toes start... the metatarsal region i guess (but this should break in)
check these threads
there are several other system binding threads too.
and here is a links that you would find eventually in the RAD boot thread that has a overly in-depth review on the RAD... but i have time and topic references in the vid description so you can jump around and use your viewing time positively