hi, they are very light and are smaller than a "standard" rotory, i mean standard very loosely as they are all slightly different in size and weight but the dodojuice spin doctor is roughly similar in size and weight to the festool rap 80 rotory which is for smaller fiddly bits of body work.
the spin doctor is a nice bit of kit and is nice and light which is good for someone moving up from a DA to further there machine polishing skills and for the price its a good one to get you started, id recomend using 135mm pads on it and not the 150mm pads as the 135s are alot easier to handle on the car and give you better feel for what you are doing,
also get yourself a few scrap panels(bonnets are better for there larger flatter area)to practice on, also find a course near to you and go along and watch a pro doing it so you can see the technique of it.
hope this helps.