I'm with Longshot cameras and obviously, I'd say target cameras are the best solution but let me give you a little background on why I feel that way. We officiate multiple ELR matches every year and have had a lot of experience with spotting scopes, magnetospeed flashers, and our cameras because of that. There are certainly pros and cons to each and I've done my best to outline them below.
Spotting scopes: work great in many cases and are the only way to see trace but they are definitely limited in the south where mirage starts around 300 yards and is an issue almost year-round, and at ELR distances you just can't see an impact.
Magnetospeed flashers: work decently well BUT they will go off if you hit short and a rock hits the target, if you hit the target frame or hanger, if your bullet skips into the target.... They also go off if you hit the target
but the only way to truly tell if you did or didn't is to walk down and check or verify it with a target camera
Shotmarker: I have used this system once while practicing at 1000 yards and the software interface is pretty simple and it seems to work well, but my biggest issue with it is that it projects my shot on a digital image of the target and I prefer to actually see my impact on the screen rather than a digital representation of my impact. It also requires calibration and a custom target frame with the microphone pieces preinstalled. Also, I believe is at more risk of being shot than a target camera. Again, I haven't used this system much so take my comments on this with a grain of salt.
Target cameras: In my opinion, this is the simplest and most cost effective way to verify impacts at long range and extreme long range. When running competitions, we have one camera setup at each target and are able to verify in real time if an impact was a direct hit, skip, or debris. You can also see misses pretty well with a target cam if setup correctly which is extremely helpful if you don't know where your shots are going. You can also mark and track your impacts with these to know exactly where your impact was whether you're shooting 100 yards or 2 miles. Target cameras also work great on paper and steel whereas the flashers only work on steel and the shotmarker only works with paper.
Longshot vs. other target cameras: There are a few different models of target cameras out there. Compared to the competition, longshot cameras are the highest resolution at 2688 x 1512 (2-3x the competition), longest range with a guaranteed 2-mile range, and sit 2-3x further back from the target than any other system. The system has rechargeable batteries with a run time of 9 hours, a signal strength indicator and comes in a hard carrying case. We also offer a bulletproof warranty for $39 that protects the camera for 2 years in case anyone shoots it. If interested in learning more, please check out our website:
www.longshotcameras.com 
