I really like the compactness and accuracy of my FX Chrono. Compared it to a Caldwell and Pro Chrono and it’s dead on with the other two. I mount mine on the end of the barrel, using the handy and quick rubber band mounting method. I made the mistake of zeroing my rifle(s) with the Chrono mounted to the barrel and that was a mistake after the Chrono was removed my POI changed on every rifle. I even trusted the groupings while it was mounted only to scratch my head when the groups opened up with it off the barrel. Some pellets wouldn't shoot worth a hoot with it mounted and it was only by accident that I tried those same pellets without the Chrono only to discover they were VERY accurate.
Here are some examples of what I am talking about:
Here are some examples of what I am talking about: