oooh well... this the 1m question.
I'm not an expert by any means but last year I took myself a nice CNC router and this is what I've learned.
1) it takes really a lot of time to master. You need to learn 3d software, CAM software and CNC control software. It's really a lot of work. So be propared
2) Economy CNC (I'd say under $5000) are rather slow with metal. It takes really a lot of time to cut a hole on a 1.5mm plate, let alone carve a keyboard case. You can quite easily work wood, plastic, acrylic and machinable wax, but metal is another story
3) Take a good motor head! At least an 800W brushless motor I'd say
4) Prefer LPT or ethernet connection over USB. I know USB seems more convenient, but it is subject to interferences. Also with LPT and ethernet you can use linux
I took mine at carving-cnc.com. the x-400 with all upgrades (especially the air cooled motor). It's a fine machine with a precision of about 0.05mm. It's not super fast and has some limits but I believe it's the best you can get for the price. Consider though that they are hobby machines.
If you have any specific question, don't hesitate to ask.
Edit: to reply to your question. being a dremel-based machine, I would not recommend the stepcraft cnc.