I have a very similar Drill Doctor in my workshop at school and it's a very good bit of kit. However, once you learn to sharpen drills by hand, you'll find that the Drill Doctor will sit unused in a cupboard for the rest of it's life.
My recommendation would be to find someone that can sharpen drills by hand on a high speed grinder, and get them to show you the basics, it really shouldn't take more than five minutes, and will save you a fortune in sharpening kit and drill bits.
I teach engineering to 14-18 year olds, and they really abuse the drills. I can honestly say that I've not used the Drill Doctor for such a long time that I'm not actually sure where it is any more.
My second recommendation would be to buy good quality drill bits. I now use Hertel bits sourced from J+L industrial and find that my students hardly ever break drills and I don't need to sharpen them half as often, whereas when we used budget drills, they were forever breaking drills, the budget drills were definitely a false economy!
Cheers
Aled