The best one I've ever used was a Suzuki made unit. It was a while ago and they probably have something better out now.
It took a bit more time because you had to set up the gauge everytime, but it was really accurate. And used a little ball rather than merc.
I've seen guys rev a bike too high and chop the throttle sucking mercury into the motor. Yeah you've got to be a bit of goof ball, but I've seen it done. I seen to remember it cost about $300 though, not cheap.
I currently use my ancient MotionPro setup(uses that dreaded mercury, but I've used it for the past 15 years), but after reading the carbtune reviews the carbtune device looks like a winner. The use of stainless steel cylinders eliminates the need for mercury and is similar in action to the steel ball method that the factory Suzuki gauges use.