I'm a big proponent of you make your own safety.
Always assume you are invisible and drive accordingly.
One, a pipe isn't heard well at all from in front...all the noise goes backwards...so you are warning the cars behind you...but they should see you anyways.
Two, headphones, loud car stereos, freaking DVDs of barney playing...people on cell phones, people freaking texting, cars being more and more soundproof... DON"T assume anybody can hear you...because they probably can't...or, sadly, don't care. I've had to kick the side door of two cars coming into my lane (not counting the endless times I've been able to brake or swear out of the way)...one time the person clearly saw me, but wanted over and was bigger and thought I would move.
So I tend to drive ahead of the traffic every chance I get...and when I can't be ahead of it, I drive like at any instant somebody is going to try and kill me...basically because it is true.
Long post short, no pipe is going to save you. there will always be cars that don't hear you no matter what. Always drive like the cars can't see or hear you. If you think your pipe or modulating lights are safety vest is going to protect you, you will be hit someday. Now good lights are wonderful. A safety vest is nice to wear. Even a loud pipe might help with a car or two...but none will make you "safe", only good riding and constant awareness will do that.
Gavin
now if they add a sound maker that projects out 360 degrees, especially in front, like a cop siren does, well that could help quite a bit more than a rear facing pipe...but again, heck cop cars with sirens roaring are often in accidents by inattentive drivers...so always drive as described above, like you are invisible.