Ask HN: Best sleep trackers?
None. Period. I was in human sleep research for 14 years as a technologist and proj manager. I tested dozens and dozens of devices- a mattress pad that claimed to track sleep. None of them are accurate.to track limb movements you need EMG attached to your legs and then to a recorder. Then a sleep tech certified in scoring must review the results.A board certified sleep doctor can get you home devices to track periodic limb movement if necessary.Acti-watches are the only devices that you might be able to get "accurate" sleep(not limbs)tracking. They're expensive and you need to buy analysis software to view results. 
I would not waste your money on any publicly available device- they wont get you the data you want.