Car and Driver did a test of performance meters like this one a few month back. Interesting read. This particular product was not tested but the same sort of foibles that these meters presented on cars would apply at least as much, if not more so, to a motorcycle application. Thats not to say that they are inherently bad products, just that it pays to know what sort of accuracy and consistency you are looking at and what factors effects their performance.
http://www.caranddriver.com/features/9380/do-inexpensive-performance-meters-work.html
