The early passive night-sights were, indeed, bulky and heavy.

However, they provided an enormous advantage in the extension of "office hours" on the battlefield.

Even just used for observation, they were, and still are, extremely valuable. Even if you eat carrots until your skin turns orange, you will never see as well as with this equipment.

The issue of concealing the muzzle-flash seems to have come late to a lot of folk; cut loose at the effective range of these early devices on a rifle with a bare muzzle, and a couple of things will happen:

The muzzle flash will temporarily "flare out" the image-intensifier elements, thus rendering follow-up a bit dubious. The flash and accompanying blast will be fairly obvious to even the most casual observer.

The US M-21 with the old Sionics muffler was very effective as the "can" disrupted and disguised the flash AND the blast. The idea is to seriously degrade the ability to locate a firer via the old "crack and thump" method. With standard ball ammo there is no disguising the "crack", but if the "thump" form the firing point is "scrambled" by the can, things get very tricky.

If you are shooting in "open woodlands", the multiple echoes of the supersonic "crack" off the trees simply adds to the confusion, especially if the muzzle-blast is diffused.

Note that there is a "muffler" kit for the Accuracy International beasties; the tactical requirement has not gone away.