Express digital ordering exercise of questionable character? (7,6,5)

I believe the answer is:

fastest finger first

I'm a little stuck... Click here to teach me more about this clue!

'digital ordering exercise of questionable character?' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'express' is the wordplay.
I cannot quite see how this works, but
'express' could be 'fast' (I've seen this before) and 'fast' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Independent.

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