I have had a Pact Model 1 for many years, which has the "brains" in a separate box that sits on the bench next to you, the "eyes" are down range. The eyes are cheap to replace. I have two friends who have other brands that have the brains down range. Theirs have been replaced several times.
There are two kinds of Chronographs ... those who have been shot or those that will be shot!! Just a matter of time. Chrony even puts a target right on the front of theirs!
Jimmy K