I got a B&Q Performance pro one years ago and it's still going strong. One thing i ought to mention, when i got it, the accessory set had small, medium and large interchangable chucks so any accessories you get from most manufacturers fit it! I usually use Dremel sanding drums for 1st and 2nd shaping on my knife scales when they are fitted. If you do go for one, try to get one with a variable speed as some materials will scorch if 'attacked' with a high speed tool.
Yes, i'd say that a rotary tool is worth it. I'd like a Dremel, but don't really know if it would give me more than i already have with the Performance Pro one.