Buy a cheap one.
Having started out with a Shooting Chrony F1 model, and then stepping up to a Competition Electronics ProChrono Digital, and now to a Competitive Edge Dynamics M2, I can tell you that you most definitely DO NOT get what you pay for. In fact, from the research that I have recently done, it seems that chronographs are all basically built from the same cheaply made bargain bin parts and sensors, and that spending more money on one may give you more flashy features, but not reliability.
I was duped into buying the CED M2 because of the manufacturer claims of being more reliable than the rest, and less prone to errors due to light issues, but I see now that I ended up with the least reliable chronograph on the market. Looking back, the Shooting Chrony gave me about the same level of errors as the M2, maybe a little less, but in that I knew nothing of the limitations of these devices, so one could say that errors would be expected. It was only when I bought the CE ProChrono that I read up on the fact that light makes them very fickle; to operate reliably, they need bright sunlight.
If you are having problems getting your chrono to read, make sure you set it up where it will have either full sunlight or full shade or, in the case of the CED M2, don't bother setting it up at all because it won't work regardless. Make sure that there are no shadows across the sensors, and if there are, put up something to completely shade them. If you are shooting rifles, set your chrono up at 12 to 15 feet from the muzzle, and maintain that distance for each shooting session.
If you have the CED M2 chrono, and don't feel like heeding my warning about not bothering with it, make sure to place the display device on a separate table several feet away from the gun or you will get crazy errors. I found out this weekend that you can shake the display on the M2 and get a reading from it despite the fact that the sensors were 15' away. On previous shooting sessions with the M2, I often got two readings for one shot, on an interval of about 1 in 10 shots. Very frustrating. If there are others shooting near you, make 20 feet or more of space in between the chrono and them, as well as the display or the M2 will read their shots too. Also, you will get readings when the wind gusts, so keep that in mind as the display will make all kinds of cool calculations for you, which don't mean squat when you have six velocity readings of 112 fps from the wind queering your shot string. Something else of note is that when I failed to get a reading from my third shot yesterday, I picked up the display and the numbers on it faded in and out, prompting me to install a brand new battery, with the same results. Not what you would expect from a $200 device advertised as being super fancy pants reliable and better than the competition.
I hope this information helps somebody. I was hugely let down this weekend as I had new loads for the 308 from my recently acquired IMR 8208 XBR powder that I believe will end my temperature and consistency problems, and the M2 chrono decided it didn't feel like working that day. Having a working chronograph for load development is a must, and I expected more from the M2 than I got. I din't get a single reading from it, so instead of ruining my test by continuing to fire the rounds, I called it a day.
That's not exactly true; I threw a great big fit about it and hurled the M2 display into the woods at a shown 324 feet per second, but at least I didn't shoot it. For some background, the Shooting Chrony met it's fate on the edge of darkness two years ago when it was not recording shots from my AR15 while shooting offhand. I started shooting closer and closer to the sensors in order to get a reading as the sun was going down until I was shooting a half inch above the unit, and the inevitable happened when I put a 55 grain round right through the display. That was an accident though. The exact same thing happened to my CE ProChrono a couple of months ago when I skipped a round off the top of the display, ruining my OCW test, which prompted me to immediately toss a C-Products magazine in the general direction of the chrono that - as fate would have it - smashed in the display screen with a perfect shot. I had no other choice at that point but to finish it off humanely with a magazine of 100 grain hardcast rounds from my Kel-Tec.
Doesn't someone out there make a chronograph that doesn't suck? I mean, damn, we can send people to the moon; we can replace a human being's heart; we can split atoms and use that technology in a bomb to end the world, and yet there's no one out there that has mastered building a device that can clock the speed of a bullet. Really?
Now comes my dilemma. CED makes an infra red light kit for the fancy pants M2 that is reported to end the problem of light sensitivity. Thinking about it though, the M2 is reported to end the light sensitivity problems without the IR kit, so I have my doubts, and there's also the issue of the display fading in and out, so their overall quality is in question. I could shell out the $90 on the IR kit and maybe have a working chrono, or I could spend the same amount on another Shooting Chrono F1 and have one that at least works some of the time, which would also allow me to take my M2 and set it on fire in the yard and dance around it in a loin cloth while screaming profane gibberish. I really like that idea. For what it's worth, when my F1 chrony took a round to the face, it still worked, except to say that the bullet hit both sensors and ruined them. So it's at least tough.
I think a nasty letter to the manufacturer is in order, and I have already left a review on the Sinclair International website where I bought the CED M2, which as of this morning hasn't posted yet. I'll keep checking that though.
If you come across this post, which I'm going to go ahead and call a Competitive Edge Dynamics M2 Chronograph review, my advice to you is Caveat Emptor. Don't bother wasting your dollar on "advanced software and digital circuitry" that was put together from Radio Shack seconds and packaged in a cool looking plastic package. Buy the cheapest chronograph you can find as they are all made from the same 1950's technology, and maybe the recent breakthroughs in IR technology will bear some fruit and make these things not suck.
*Update* I found this post on Sniper's Hide about folks building their own IR light source as the kit from CED doesn't sound all that reliable.