add G2A windows license support (at least as an option)
G2A is legit and gets you a much better price. Though some people dont trust it so maybe have it as an option just like MIRs.
Although G2A keys will work, the nature of the site means that anyone can sell whichever keys they want. The only legitimate way to get windows below retail price is with a student discount.
The people selling keys on G2A will likely be selling volume licensing or student keys which means that you are breaking the terms of service on the licenses by using them.
For this reason I cannot recommend them.