http://www.longrangehunting.com/forums/f19/new-oehler-35p-new-skyscreen-rail-first-test-data-60778/
This link will lead to a Thread that will give you a feel for the accuracy potential of chronographs based on data - not D.ID's or other's opinions. They can be accurate and consistent. They will all, occasionally, record an errant velocity. If you buy an inexpensive one with only one velocity recorded per shot, then you'll often never know if you received a bad velocity. As soon as I starting running two chronographs concurrently, I recognized that I would never again run a single chronograph. The Oehler 35P is the only factory chronograph I'm aware of that provides a 'proof' channel feature which provides the second recorded velocity for each and every bullet fired. My setup now provides me with four velocities for each bullet fired. I'm able to identified flawed data when they occasionally occur with this setup.
Are they worth it? Depends on your interest and application. D.ID tells you no. It would appear he experiences huge disappointment when others don't agree with his findings and conclusions. Not just with respect to chronographs. So I've given you a link to some examples of data recorded with my chronographs and you can reach your own conclusions and opinion about what might be best for you. If you're interested enough to complete the entire Thread, then maybe you'll appreciate owning and using a chronograph. If not, you may not find the cost and benefits and time to be 'worth' it.