I like the PX100 I bought refurbished for $17 on ebay, but the left ear-piece kept falling off right from the start. It wouldn't go back on and stay, so I had to hot-glue it in place. Now the right one is falling off all the time, and the left isn't as comfortable because the glue job is 1mm off from the right position. I liked them enough to buy another pair for $19 (shipped $26), but I am afraid to use them in case they'll fall apart too. The PX100 sound pretty good to me, with some coloration in the upper mids though - the bass seems to be nicely extended for an open ear headphone.
I also got some PMX100 for about the same price, which are a behind the neck headset, and they don't sound anything like the PX100, and wonder if I got a bad pair of PMX100. Also, the earpiece attachment point seems just as flimsey as the PX100 that fell apart.
So, is this a typical problem for the earpieces to pop off the head band so easily? I love how my iGrado are built like a tank (and sound better), but I don't like the two wire cord running to both earpieces. I was going to use these in the car or shopping, when I need to be able to hear what is going on around me.