There is a post here regarding the accuracy of drop weights being much better than expected, even if you don't get them 100% parallel to the floor...being within 10% of desired resulted in insignificant differences from desired tension. I can't find the post, since the webboard SW upgrade the old link to the post goes to the wrong place now....I got a drop-weight, the additional $ for a crank didn't make sense for me, given the relatively small number of racquets I'll be stringing.
Check out the Alpha Pioneer DC, and the Gamma drop weights, I liked them the best...bought an Alpha.