teckel:
Can't wait to get the sensor and figure out what's going on. I hope to test and send back ASAP.
I'm still amazed you're volunteering to do this 
That's dedication!
If you find that the SR04 that I sent you behaves significantly differently than the ones you have, I would be happy for you to keep it for regression testing purposes. (I could potentially help write a regression test, too, although I've never tried making one for an Arduino library, and it couldn't be fully automated due to its nature.) I have a spare SR04 anyway, and they're cheap enough that I could just order more if I wanted more.
teckel:
With properly working sensors, a virtual sensor from multiple sensors should not be required. Sensors that actually work are very reliable and give consistent and accurate readings all the time. I also have sensors that "work" but are clearly not 100% functional (this is with any library). Mine having a problem seem to work to around 50cm, then get all wonky.
The sensor I'm sending you works up to 100cm (I didn't try longer distances), but it occasionally throws in an outlier of some kind, whether it's an in-range but wrong value while something is in the sensor's range, an out-of-range value while something is in range, or an in-range value while nothing is in range. I agree that if a sensor is working properly, it shouldn't do this. My original idea was to use virtual sensors to combat inherent unreliability issues with these cheap sensors (much like RAID was created to create reliability out of unreliable cheap parts), but if there are reliable sensors in the same family for the same price, I think I should just use those
teckel:
While I find that my SRF05 and SRF06 are more reliable, online I've also found at least two totally different kinds of SRF05 sensors. Both have the same model number on them, but each are electronically different with different pinouts. So, I don't want to totally endorse the SRF05 as superior, as it appears they're made my multiple manufactures with different specs. Which is probably why there's some HC-SR04 sensors that "work" and probably why the HC-SR04 sensors you have don't work with my library, as they're made by a bunch of different manufactures, with different specs or quality control.
Hmm. Any such variations with the SRF06 sensors?