My option on the matter is that it is easier with straps, BUT you pick up pretty bad pumping technique. 

Most guys I know that learned to pump with straps and still go strapped, have big problems pumping strapless , whereas guys who perfected their pumping without straps can really pump long distances with straps.

I personally hate straps when pumping as they limit you my trapping your front foot in one position.  I move trim the board quite a bit with my front foot position when pumping, especially in light wind take offs with the wing and I can get a lot more out of the foil doing that. 

I tell people to learn to pump without the straps first, and then use them later if they want to. That way they will have good technique.

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Gunnar