Tried it and then sold it on my 12s. Helps a little but is annoying to have on there. I can get about the same effect using some of my fingers to grab the brim of my hand for a little more steadiness off hand.
I like the foreheads rest. It’s not a gimmic! It’s kind of like grabbing your baseball cap brim when you need to bear down and get steady. I have the forehead rest on both my NL’s and on my EL range TA’s.
I’ll go against the consensus and state that it absolutely is a great addition to the NL’s. I’ve had 10x32’s and now 10x42 NL’s. Not only does it steady even the 32mm NL’s significantly, it allows you to fine tune the eyecup height position in order to get the maximum amount of FOV out of them, without getting blackouts. Even while using them on a tripod, it helps with this as well.
I think if you are using NL’s without them, you are shorting yourself on all the benefits that the system offers.
I tried it and didn’t find it did anything I couldn’t do myself so I returned it. One of those things you have to try for yourself. Just buy from a place with a good return policy.
I have it on my 12s and really like it. I dare say if I didn't have the forehead rest I probably wouldn't want to freehand the 12s and I'd sell them for 10s.