Try perhaps:
=SUMPRODUCT((B1:B10<>"")/COUNTIF(B1:B10,B1:B10&""))=1
this will return TRUE if all values are the same in B1:B10 (doesn't matter the value).
If you have blanks within the range and want to return False if any are blank.... then
=AND(COUNTBLANK(B1:B10)=0,SUMPRODUCT((B1:B10<>"")/COUNTIF(B1:B10,B1:B10&""))=1)
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