Compare 2 tables easily - how do you do ?

I got the following result in less than 1':

you have to group by Customer field both table NEW and OLD:

then produce the difference Table:

let
    Source = Table.NestedJoin(OLD, {"Customer"}, NEW, {"Customer"}, "NEW", JoinKind.LeftOuter),
    #"Expanded NEW" = Table.ExpandTableColumn(Source, "NEW", {"cust"}, {"NEW.cust"}),
    #"Added Custom" = Table.AddColumn(#"Expanded NEW", "diff", each diff([NEW.cust],[cust])),
    #"Removed Other Columns" = Table.SelectColumns(#"Added Custom",{"diff"}),
    #"Renamed Columns" = Table.RenameColumns(#"Removed Other Columns",{{"diff", "cust"}})
in
    #"Renamed Columns"

which use this function:

let
    diff = (old,new)=>
    let
    names=Table.ColumnNames(old), 
    mm=Table.TransformRows(old,  (rowOld)=> Record.FromList({"Difference",rowOld[Customer],rowOld[Product]}&List.Transform({3..20}, each let rowNew=new{[Product=rowOld[Product]]}? in Record.FieldValues(rowOld){_}-Record.FieldValues(rowNew){_}),names))
    in Table.FromRecords(mm)
in 
  diff

and finally put all together:

let
    Source = Table.Combine({OLD[[cust]], NEW[[cust]], Difference}),
    #"Expanded cust" = Table.ExpandTableColumn(Source, "cust", {"Scenario", "Customer", "Product", "Val Driv 1", "Val Driv 2", "Val Driv 3", "Val Driv 4", "Val Driv 5", "Val Driv 6", "Val Driv 7", "Val Driv 8", "Val Driv 9", "Val Driv 10", "Val Driv 11", "Val Driv 12", "Val Driv 13", "Val Driv 14", "Val Driv 15", "Val Driv 16", "Val Driv 17", "Val Driv 18"}, {"Scenario", "Customer", "Product", "Val Driv 1", "Val Driv 2", "Val Driv 3", "Val Driv 4", "Val Driv 5", "Val Driv 6", "Val Driv 7", "Val Driv 8", "Val Driv 9", "Val Driv 10", "Val Driv 11", "Val Driv 12", "Val Driv 13", "Val Driv 14", "Val Driv 15", "Val Driv 16", "Val Driv 17", "Val Driv 18"})
in
    #"Expanded cust"

PS

you could find usefull place some if.. the .. else  in the function to check case where new and old doesn't match!