I have both the yellow and grey handhelds.
I have had the yellow for much longer, it's decent and does the job well. The only thing that is a downer is you have to press the button each time you wish to fire. This can be a nuisance if you are adjusting the velocity, and is more frustrating when a few of you are checking. But it is vastly better than going to the back of the chrono queue each time.
You can dangle it from the barrel but I have had best results holding it at the barrel, and it does not fall off if you hold it!
I have not used the grey much yet, but you don't have to keep pressing the button, and it has FPS but I'm not so worried about that. You cannot hang the grey off the marker but that does not bother me.
For a bit of info the manuals for both are as below.
Yellow
Grey
http://lh5.ggpht.com/_pY3HXrpCAQs/SUK9W6W76vI/AAAAAAAADXM/vlaZA03N8mc/s800/x-radar-chronograph.jpg