Having had several checks collected from me by (typically) utility companies in order to set up automated payments (where the company withdraws funds instead of my initiating a payment each month), I always gave them a blank pre-printed deposit slip with the bank routing number and personal account imprinted on it in magnetic ink. One
company demanded a blank voided check in lieu of the deposit slip, the others were quite happy with what I gave them. Since all that is wanted is the numbers, preferably without the digit transpositions, skipped digits or extra inserted digits, or outright substitutions that far too many customers inadvertently (or advertently) make when filling out forms,
I don't see that it makes much of a difference whether it is a deposit slip or a
check that is collected, nor why having a check filled out and then voided instead
of just a blank check marked "VOID" is better. Of course, if they demand an original
check that has been cashed (to prove that the account is active), that may be hard
to do since most (all?) US banks no longer return cashed checks to their customers.