DAX measure use Month Number as value to return true / false

Hi, I wanted to use the monht nuumber as a true / false criteria in a measure, my starting point was

ALLMONTHS :=
IF (
    ISFILTERED ( 'Calendar'[Month] ),
    CONCATENATEX (
        VALUES ( 'Calendar'[Month Number] ),
        'Calendar'[Month Number],
        ""
    ),
    BLANK ()
)

This gives a count of 1 to 12 in a pivot and works perfectly well with say [TotalSales] / [ALLMONTHS] ,

but if if try and use it with an IF ;

  Xmeasure:=IF( [ALLMONTHS] < 4 ,"X" ,"Y" )

I get an error, I sort of get why this does not work but is there another ( hopefully simpler) way to get a true / false from the month number,
ive attached workbook to give some context.

Richard.