Everything you need for baby and nothing you don't
First off, it’s ridiculously hard to sort out how to hang mobiles. You either get one that hangs from the ceiling, in which case you need a very tall stepladder (not a good combo with pregnancy) and a lot of confidence that you’re hanging it at exactly the right height for baby safety (no tangling in strings) and in a location that you will never need to change (see: stepladder + aggravation). This is well nigh impossible. Get OK with the fact that you’ll be up that stepladder again when Junior decides he prefers to hang out at the other end of the crib.
If you decide the kind of mobile that attaches to the side of your crib or playpen is more versatile, good luck finding one that you like and fits onto your crib. In my experience, if you have a Graco crib, the only mobile that fits onto its rail is a Graco mobile. If you have a snazzy crib that you love, there will be no mobile that fits its rail and you will have to resort to some Rube Goldberging of this “one size fits all” arm thing with the mobile you like. Which, naturally, will look like you sorted the whole thing out while you were drinking and will undermine that whole “cool minimalist parents” aesthetic you were going for.
Second issue: babies with poor eyesight (all of them) can’t distinguish the tasteful, muted colors of that Eames-ian mobile you found at that great baby boutique in Chelsea. I’m not saying you shouldn’t get it. Be my guest. I love it too. But little Theodore Pancreas III will not be able to appreciate it for many months. What you want up front are either black and white patterns or, shortly thereafter, primary colors that are easy to distinguish.
In both of these case, Manhattan Toy is there for you again: the Skwish Mobile has a crib-agnostic arm that screws into place on pretty much any crib rail (and can be moved) and the basic, bright colors are ideal for your little new addition to the world.
So I love it. Try it: you might too!