I purchased a Milestone from Target today in an attempt to solve a few carseat puzzles in our fleet. I have to say at unboxing I am pleasantly surprised. It takes up less room front to back than my Classic Marathon (or SK XTSL with AA), and yet, affords a significant amount of greater shell height over the Britax. So far, I'm a fan of the low sides (not quite Radian/Diono low), but allowing lots of clearance for rear facing toddlers/preschoolers who load themselves in and out. It is at least as narrow as the Classic Marathon, but I have not measured and I'm not sure how it will be for puzzling situations. I believe I had read it is more narrow than the Clones (which are supposedly 18") and possibly as narrow as the 4ever (though I'm not sure…) Creature comforts seem adequate--I like the foam-like padding and the velvety soft infant insert. And my son will be thrilled for his own cupholder like his big sister! It installs quite upright via LATCH, even in the first recline position, in our 2010 Jetta Sportwagen. This is fine for my rear facing 3 year old--but not so much for our future infant. There is a level line that is supposed to be level with the ground when rear facing (can this be parental discretion?); I haven't looked at it thoroughly since I switched from recline position 2 to 1 (as it is on the other side of the carseat from where I was working--and I'm parked on a slight incline). I'm going to get out the angle meter on the iPhone to see how it's doing. Will also plan to install in our 2014 Odyssey for comparison sake!
edited to add: the cupholder is removal and can be installed on either side of the seat.