I started out routing pcbs with a spindle powered by a dremel and a solidly mounted, heavily modded, flexi-shaft hand piece. I've posted pics of it elsewhere on here. I think one of the bearings gave up the ghost a while ago, but even before that I was getting inconsistent results. Sometimes the routing would be perfect and the bit would last forever. Other times it was total garbage and the bit would break, even at low feed rates.
I finally sprung for a k2 mount for my porter cable 6902 and the collet kit from thinktink. The results are very impressive, even with a bit that's lost a tiny part of it's tip. I should be able to push the feed rates back up now and hopefully I won't be running through the bits as quickly.
I measured the dremel-diy spindle and I was seeing as much as .01" TIR, whereas with the new setup I'm getting less than .0005" TIR. The dremel-diy spindle varied quite a bit every time I would re-seat and tighten the collet. My dial indicator only has a resolution of .001, but I think it's safe to say the change gives me at least an order of magnitude improvement.