I think that only experience (or luck) will help you avoid problems when etching logos. As for the machine, I would suggest variable power so that you can adjust the voltage and avoid burning up your stencils. Also, the ability to easily switch from AC to DC is helpful. DC power removes metal, and AC power produces a black mark. So if you can etch deeply in DC, then readily switch to AC to make the mark black, you can save some time. Personally, I am still struggling with this procedure. After I get my dark mark I clean the blade with the recommended cleaning solution. My blades don't rust, but annoyingly the fluid invariably removes the dark coloring. I have taken to carefully applying one of the instant bluing solutions to my mark. I am thinking about trying the engravers enamel but it's kind of expensive.
As, or more important, than having a decent machine is having good stencils and using the proper etching solution. They make all kinds of solutions for all kinds of metal. They are material specific (or so they claim). I have had stencils made by Marking Methods and they work well. Unfortunately, from what I've read here recently, MM isn't too keen on helping knifemakers these days. There are plenty of other places to get stencils though. I was finally able to pick up one of Etch-o-matics stencil making kits on ebay, so now I just make my own. They have worked pretty well so far.
:thumbup: 
