I'm not sure if it's the right forum either, but what the heck.
I've used Telex 750s in a variety of real and simulator cockpits. Pretty much universally I've found that the complete lack of noise attenuation annoys me, raises my stress levels, and reduces my (already arguably average) working effectiveness. I rarely use them now, save where there's a good reason to be regularly talking off-mic to other people in the cockpit, and then for only short sorties.
G