I prefer this $20
Outlet to Go strip. It includes three grounded plugs, a USB charger, can be used internationally, and (unlike the little cube) won't conflict with other users of the same outlet. Also, this one works better with "wall warts" that have a heavy transformer attached to the prongs. On the con side, this one is more expensive, heavier, and bulkier than the little cube.
Using 3 prong to 2 prong adapters is generally a bad idea, unless all devices you're using don't require a ground.