I bit the bullet today and bought 3 full kits. Nextbase 522GW + rear window mount camera + hard wire kit. One set is for my daughters' car so if I'm lucky I might get the money back for that one. Come to think of it I might fit that first and use her Fiesta as guinee pig.
I'm not concerned about the GLC but my wifes' Mini clubman will be a bitch when it comes to the rear camers as the split doors pose a problem - should be fun.
As an aside, Nextbase are currently running a promo through retailers for the 522GW at Ł119 and the modules at half price if bought with a dash cam, can't get much better on line so I called in to Curries to handle the cameras and try to negotiate a price as I was buying multiples but was told politely to sling my hook in contrast to Halfords next door who were delighted to do a deal.