Measuring your drop isn't always possible for many people, simply because they don't have access to ranges over 100 yds. If you do, that's about as good as it gets for accuracy.
Magnetospeed units will be close but they can and do vary between units. Same goes for Chronys. Identical conditions, side by side, same rifle and the readings can be very different. No, I'm not talking about 25fps.
I find the Magnetospeed units gives less variation between units.
When all is said and done, measuring drop at given ranges may just be the best way to measure velocity of a given load. I know that when I was still shooting HBR, it was my go to method.
The Chrony was basically to make sure my loads were consistent and in the ball park.
