most Mandate-Palestine 20 mil coins are tough particularly in mint-state (1933, 1934, 1941). However, before buying any I'd make sure they've be professional graded as a large number of Mandate-Palestine coins are "cleaned" or processed in some way. I use NGC, PCGS or ICCS to grade them and am quite pleased at the outcome.
The series is tougher than most think if the coins are properly graded.