in update 0.9.5, the armor penetration of GERMAN destroyers 150 mm HE shells was increased from 25 to 38 mm, and this is WITHOUT IFHE
so IFHE is NOT NEEDED on German 150mm DDs. shells already penetrate almost all ships up to tier 10 (except for German battleships), even the boardside and deck of American BBs.
IFHE gives a penetration of 47 mm, which is completely unnecessary, since it additionally allows it to pierce only the boardside of the Gneisenau.
Since the armor penetration of GERMAN DDs 128 mm HE shells has also been increased from 21 to 32 mm, the need for IFHE is questionable, as even without it, they can penetrate almost all cruisers up to tier 10 (except for Moscow) and most BBs (except for German ones or the boardside and deck of American ones).