Never used them for their designed use, ie, sleeping . On the bike they don't block sound out completely. They definitely dampen helmet noise significantly but I still hear what I should hear when riding and the intercom is clear.
I use an Interphone system, very happy with it. I always wear ear-plugs so have no idea what the system is like without them.
When I say ear-plugs, I actually use 'Boots Soft Silicone Earplugs'. They are perfect for me, easy to mould for a tailored-fit.