I have the 750.
Drilling habits are a huge factor. I always try to gauge the remarks of someone's opinion against their actual usage. One guy's worthless is another guy's treasure.
I regularly make things with metal and thus do a fair bit of drilling in it. If I were only drilling wood all day, maybe I wouldn't care as much. But I won't buy a bit I can't sharpen easily. I don't use brad point bits because they hold little value for me. Some guys love 'em, but they're a one-trick pony and when they DO get dull, you're kinda stuck or at the very least it's not a simple task to sharpen.
So with that said - In my shop, where I primarily use standard jobber bits to drill steel, aluminum, brass, wood, plastic, etc... the Drill Doctor is invaluable. I'm also very cheap. If you only use twist drills, you can sharpen 'em for a LONG LONG time so the cost of a good set of bits is easily offset after two or three sharpenings - and a twist bit has a lot of flute, you can get dozens of sharpenings from a single bit (sometimes hundreds). The appropriate cost comparison is the Drill Doctor to at least 10-15 full sets of high quality drills. It's easily a cost savings in that regard.
The only reason I replace a drill bit is when I break it. And I find the more I keep them sharp, the less often I break them.
If you like standard twist drills and work in metal fairly frequently, I think you'll absolutely benefit from one.