Superfluid circulates without drip - that's handy (6)

I believe the answer is:

useful

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'that's handy' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for useful that I've seen before include "Very able, competent" , "Utilitarian" , "Beneficial" , "Advantageous; very able" , "Suitable for practical purpose" .)

I've seen this clue in The Irish Times.

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