not trying to rain on your parades, but its not a legal headset for use in the 121 environment. The LS Mach-1 is not TSO'd... however, your buddy w. the Sennheiser HMEC-25KAS is onto a good thing. If you work for an alpa carrier you can get the sennheisers for a cheap price directly from sennheiser. Awesome headset, and its not a legal issue...