Crib mobiles - necessary or not?

Ke
My hubby and I are on the fence about getting mobiles for our twins.  One, we have mini cribs so not all mobiles may fit on them. Two, since there's two of them, I wouldn't want to play music since they wouldn't be synchronized.  
We also don't want them to lose out on the benefits of mobiles like motor skills and stimulation.  
I was thinking of making my own.  Anyone try this?
Thanks for the feedback!!

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