With childminders, as with any other form of childcare, you must listen extremely closely to your instincts. This is not so much about child safety, but about what you can stand. If you find yourself intimidated by the cm, or dislike something about them, but think that because s/he is a professional s/he must know better, forget it.
Vouchers: do you work for a large firm who want to offer this to many employees, or a small company who are setting this up for you? As far as I can tell, there is no actual need for an intermediary voucher company at all, although it's easier for you. What happens is that you get your payroll dept to deduct the amount you want from your salary (maximum was £273 a month the last time I did it, but it changes). This appears on your payslip as a salary sacrifice, i.e. reduction in your pay before tax, theere's a box for it on the slip, and obviously it comes off the total! The childcare provider then invoices your work, and your work pays the invoice with the money they have withheld from you.
Don't forget that you and dh can both sacrifice anything up to the maximum amount s
from your salaries in the same way, so that you can jointly pay up to £546 a month like this.
Your childcarer must be Ofsted registered to get paid via this scheme, but all childminders are, this is only an issue if you decide to go for a nanny or nannyshare instead (don't rule a nannyshare out, it can be great, esp if you don't find a childminder you really like).
So I don't really see why your childminder shouldn't be able to just invoice your employers directly, eliminating the need to pay the voucher company their whack. But the childminder may or may not be happy to do this, and I never quite managed to set this up myself, i always did it via a company. The person to get on your side is the management accountant or the payroll person as they have to sort it out. The employer saves money on the employers' natioanl insurance side, so it shouldn't cost them much if anything.