The micra is more like a small pocket tool than a keychain tool, in my opinion.
Anyway, the micra has bigger scissors, not as precise as the the classic, but tougher.
The classic has easier access to the blade, while the micra offers a bit more tools.
The rambler screwdriver/bottle opener is superior to many small Philips screwdrivers, and it works on a variety of screw sizes.
The tweezers on the micra are narrower, and a bit more awkward to use, mostly because of the way they are attached. They work though, no problem there.
The scissors will even cut zip ties, but they won't be as precise in detailed work as the classic's.