Over the years, i have used several Chronys, a CED M2, and a Magnetospeed. The first two Chronys expired from "lead poisoning", so buying a unit where replacing the sensors is not too expensive is a plus.
Of the chronographs that have used that use some kind of optical sensor, getting the chronograph to "see" the bullet can be a challenge at time. The position of the sun in the sky, position of the sensors to the sun, cloud cover, caliber of the cartridge, distance of the sensors to the muzzle, and several more issues can all give fits to the sensors.
There are several troubleshooting aides out there. The Chrony's instruction manual has some good suggestions. With my CED M2, I finally bought the infrared lights and virtually all of my sensor issues have gone away. Of course, you now have to make sure the lights batteries are charged.
Currently, I have been using the Magnetospeed chronograph. So far, it has been the cat's meow with rifles and jacketed bullets. No sensors down range which adds some flexibility to its use. Down side, it does not work with handguns and I do not know how well it works with cast bullets. The chronograph has sensor adjustments that are supposed to read cast bullets but I have never tried shooting cast over my Magnetospeed.
The M2 and the Magnetospeed chronographs have a method of downloading data directly to a computer, which I like. But, this feature is not necessary.
In my opinion, most of the differences between the different chronographs are in the features the chronograph offers. The Ohler (spelling?) has an excellent reputation but that comes at a price.
Hope this helps.