Could you just as well have said, "The Magnetospeed tracked within 6fps of the highly accurate Caldwell at most and mostly averaged within 2fps, which is not bad at all."?
In other words, I'm wondering if you have any evidence that one is more accurate than the other? I couldn't find any accuracy claims for the Magnetospeed, but the tests they publish on their web site show that it's within about a half a percent of the results reported from an Oehler unit. That's not bad, but the Caldwell folks claim their units are calibrated to within a quarter of a percent. Does that make it better? Hard to say.
Of course, manufacturers don't always tell the whole truth, but I certainly wouldn't automatically give the nod to one or the other without seeing something better than what the sellers claim. I think it's fair to say they're both good, but as for which one is more accurate, that's not a slam-dunk, at least for me.
The Magnetospeed is easy to set up but it's a lot more expensive than the Caldwell and I'd expect that it will effect the group size one way or another making it undesirable for load development. Since that's the primary reason I to the trouble of setting up a chronograph, I'm pretty sure the Magnetospeed doesn't make sense for me. It sure looks easy to use though.