They are pretty effective but do screw up your normal night vision if you are not careful how you use them. Stick to using the same eye & close it when looking thro the other eye with normal sight. There is some distortion around the edge of the lens but you can see as if it was day light & there is even an inbuilt IR light for relatively nearby detail in total darkness.
-------------------- Boaty junk clogging up your shed or lockers? Chuck it in Marinaskip