I used them occasionally in the military, my recollection is that everybody liked to complain about them, but they got the job done. They are heavy, and a little slow to use because shutter cocking and film advance are not linked. A lot of folks claimed the rangefinders were prone to getting out of adjusment, but I never saw any direct evidence of that. OTH they have great optics and are relatively simple which are attributes with great value.
Later in the USAF, they were replaced by Koni Omegas, not much lighter, but much faster handling, which was nice.