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There are three basic types. Optical, magnetic, and radar.
Each has pros and cons.
Optical is the least expensive. It takes more setup and can have some errors when lighting conditions vary.
Magnetic is accurate, but must hang a sensor bayonet on the muzzle. The bayonet can be difficult to adapt to some guns. Middle of the pack in cost.
Radar is accurate, easy to set up. The Bluetooth is flaky, and you tend to need an external trigger to reduce missed shots. This is the best but most expensive method.
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This pretty much sums it up. My only add is that Optical data quality is the least consistently accurate. When properly set up, they can be just as accurate anything. The trick is there are a lot of tricks to "Properly set up". I tended to quite a bit of variability in readings from one outing to the next, with optical. Less so with radar. Though even with Radar, if you set up a bank of targets, the reading you will get on the perfectly centered target and the reading you get on the far right target, may not be the same.
Of the options, the age-old case of the more you spend, the more you get, comes into play. If you just want something on a budget that you'll use only a couple times a year, optical is the way to go. I like to tinker, and to date have probably close to 5000+ traces tracked on my LabRadar (one outing = 10 test loads at 5-10 rounds per load, so each outing can get you 100 traces). And I can set it up, and just roll. With the others, there's a lot of set-up/screwing around time. With optical there's a LOT of screwing around time (done downrange - looking back at your muzzle to check alignment - yay!) With magneto, you have to remount on every gun being tested that outing; and you can't really trust the impact data from those shots, because you were touching the barrel while firing.
To me, Magneto is actually the worst choice, because just save the moeny and go optical, which is more general, or spend the money and go Radar. Just my own logic, Iwill say Magneto does give good data.