did bit of searching
Based on what I understand from JG 7 The World's First Jet Fighter Unit 1944/1945 by Bohme the answer is not very common. Apparently the new gunsight was tested with the Me 262 by III./JG 7 in late February and early March 1945 after which Major Rudolf Sinner, the Gruppenkommandeur, decided against equipping the aircraft of the unit with the device. Evidently the high speed of the jet fighter allowed very little time to adjust the range controls for the gunsight to compute the necessary deflection. The book mentions that very likely the only victories claimed by a Me 262 equipped with the EZ 42 occurred when Unteroffizier Heiner Geisthövel of 2./JG 7 claimed two P-51 fighters on 8 April 1945. In contrast to the negative opinions concerning the use of the EZ 42 with the Me 262 it is my understanding that the pilots of II./JG 300 equipped with the Fw 190 A-8 that used it operationally were pleased with it. I hope this helps.
EZ42 Luftwaffe and Axis Air Forces
forum.12oclockhigh.net
features the EZ42 gunsight... "white 4", WNr 500226, of Oberleutnant Bohatsch, 1.JG7 at Dedelstorf. Bohatsch landed there on 8th of May 45 coming from Saaz/Zatec.
Nice pic of an Me262 on eBay Luftwaffe and Axis Air Forces
forum.12oclockhigh.net
As I collect gunsights, I constantly look for the EZ42 among others in all pics I come across. In the last 10 years I have found pics of it installed in only four aircraft. If there's more please be so kind as to post them.
EZ 42 in FW 190 - Luftwaffe and Allied Air Forces Discussion Forum