I've never tried to email Trend... though I have spoken to them on the phone several times, and got through to a real person right away each time. Trend customer support is, in my opinion, great.
However, as you know, I also rather like the 3M units.
Tomorrow I'll make some photos of the Lithium Ion battery that I've hooked up to my 3M Airstream. I'm very pleased with this setup, as the battery is lightweight (4 oz) making it easy to mount atop the helmet (so no cord to the waist).
Lathes: Nova DVR XP, Delta 46-460, Jet 1014vsi; Bader III 2"x72" belt grinder; Triton 2.25 router; CMT Industrio table; Jointech fence; SC planer; Dewalt miter; Delta 14" bandsaw; Festool TS55, MFT/3, CT22, ETS150/3, OF1400, PSB300EQ, CXS; Hegner Scrollsaw; JJ-6CS jointer; Grizzly 1023s cabinetsaw, Jet 17" drill press; Rigid OSS; 9" SandFlee; 3M AirStream & Breathe Easy PAPRs