If straight line speed is all that matters to ya' that's the cheapest way.

Neat thing about the devices are they'll give you the entire flight results. Wanna' know which prop was pulling best on the verticals without having to vote everybody's opinions? Wanna' know just how much each prop slows over the tops of loops?

Seems to me that the only limit on what it'll tell ya' is what you choose to ask it. For example, you could compare stall speeds. You'll have the speed graph right up to the point of the stall.... and beyond. Just one example there.

Will it be for everyone? Seems it oughta at least be for people who want to play with decently reliable data. Surely beats guesswork. But it's sorta like a tachometer. Or a wattmeter.