DAX code for comparing two tables, and showing the differences - Is it efficient enough?

Hello guys,

I have two tables, with the columns: 
CustomerNumber, InvoiceNumber, Amount, Key (the key column is "invoicenumber & amount")
I compare these, and with DAX formula, i get a new table with the differences. 
Can somebody check if the code is "efficient"?

I cannot to it in Power Query because one of the tables are a api query which uses 30-50 minutes to run, and it can time out i was told. Either way, the code below works fast. 
not sure if it is efficient enough.

SAP_InvoicePartner_DIFFERENCES = 
VAR SAP=
    CALCULATETABLE(
        EXCEPT(
            VALUES('SAP Invoices'[SAPKEY]),
            VALUES('Partner Invoices'[KREDKEY])
            ),
            INTERSECT(VALUES('SAP Invoices'[CustomerNumber]),VALUES('Partner Invoices'[CustomerNumber]))
    )

VAR InvoicePartner=
    CALCULATETABLE(
        EXCEPT(
            VALUES('Partner Invoices'[KREDKEY]),
            VALUES('SAP Invoices'[SAPKEY])
            ),
            INTERSECT(VALUES('SAP Invoices'[CustomerNumber]),VALUES('Partner Invoices'[CustomerNumber]))
    )
RETURN
UNION (
GENERATE(
    SAP,
    CALCULATETABLE(
        SELECTCOLUMNS(
            'SAP Invoices',
            "CustomerNumber",[CustomerNumber],
            "InvoiceNumber",[InvoiceNumber],
            "Amount",[InvoiceAmount],
            "Kilde","SAP"
            )
        )
    ),

GENERATE(
    InvoicePartner,
    CALCULATETABLE(
        SELECTCOLUMNS(
            'Partner Invoices',
            "CustomerNumber",[CustomerNumber],
            "InvoiceNumber",[InvoiceNumber],
            "Amount",([InvoiceAmount]),
            "Kilde","InvoicePartner"
            )
        )
    )
)