In all honesty, I do not own a MultiPro, nor have I ever used one either. Although I do often use my dads old variable speed, corded, Dremel tool which he uses a lot as well and has had it next to forever. However when I wanted to buy one, I didn't have a lot of cash at the time so I got an inexpensive variable speed 9.5v rotary tool kit that has a shaft mounted LED light, several accessory attachments, including a flexible extension shaft from a well known discount tool retailer. I got this tool knowing that I'd get what I paid for which was roughly around $20.00; so my expectations weren't very high. And while admittedly, the tool has lasted longer than I initially anticipated (2 years now), the rechargeable battery pack is holding less of a charge with each use, it runs rather hot & combined with the other shortcomings it has; makes this tool a real displeasure to work with and pales in comparison to using my dads Dremel.
So getting to your question, my first advice would be to buy the tool new; you never know what the previous owner did to or with the tool, not to mention you should want a warranty when buying any rotary tool. Second thing would be determining how frequently you'll be using the tool, if you feel this would be quite often; then buy the best tool you can afford! In regards to buying a cordless tool, I'd advise against it unless it has the ability to also be operated with an AC\DC converter power pack cord. Only because unless you have a second battery to use when your first one is charging; I think that you'll find that ANY cordless rotary tools battery doesn't last very long. And dealing with a cord isn't that troublesome if you have an extension cord and a hook to hang the cord from allowing the tool to hang down into your workspace. You'll agree that a cord isn't that bothersome when you have to wait at least 3 hours to finish just a little bit of work that couldn't be done because your battery died. And lastly, I think single speed tools are often too much for alot of tasks and strongly recommend at least a two speed if not a variable speed tool. These are just my opinions and what I've experienced with rotary tools, I hope you find it some help in choosing yours.