The Sharpmaker is a great, easy to use system but has limitations. As Tizwin says, it's not a good tool for reprofiling. It has 2 "settings" -- 40 degrees and 30 degrees. All of the Spydercos I've ever owned have edges well under 40 degrees so it works beautifully with them. Other brands are hit or miss. I'd say more than half come with edge bevels more than 40 degrees, especially near the tip. When that happens, the Sharpmaker won't do the trick, unless you're willing to spend hours and hours on the job (I did it once with a Benchmade 710HS, and that was enoughh for me).
I have the diamond rods. First, they're about 320 grit, which is faster cutting than the medium rods (about 600 grit), but still very slow. Second, mine seat themselves wider in the stand than the other rods. So when I've refrofiled with them in the 30 degree setting, for example, the other rods don't come very close to hitting the edge. In short, if I had it to do over again, I wouldn't get the diamonds.
What has worked well for me is to reprofile freehand using an extra course DMT diamond hone. Thin the edge way down with the DMT, then establish and maintain a micro-bevel with the Sharpmaker. You're first freehand results might be a little ugly (mine sure were), but they will look better with practice. For a perfect edge I think you need an Edge Pro -- I have one on order.
I also have the ultra-fine rods. I have found them to be worth it, but all they do is give you a more polished edge. A more polished edge is better for push cutting, while a courser edge is generally better for draw cuts. Really, the regular fine stones will give you an edge that's useful for a lot of cutting chores. For some knives, like kitchen knives, I stop at the mediums, or even the diamond rods.
Go ahead and get the Sharpmaker -- it's a great tool. But understand its limitations or you'll be very frustrated.
