In case anyone's wondering, PJRC is absolutely *not* going to pull a FTDI-style move to intentionally brick counterfeit boards.
I am going to write some code to detect these boards. Future Teensy Loader versions will show a warning message. I might add something to the linker script to encode the CPU speed setting into the .elf file, and then have Teensy Loader prevent known-to-brick images from being programmed. The absolute last thing I want to do is hurt people who unknowingly purchased a counterfeit product.
But I have no hesitation to make the warning dialog annoying.
I probably will make it pop up every time code is uploaded. If I'm feeling nice, I might go to the extra effort to make it non-modal. Maybe...
My main goal with counterfeits is to make everyone who purchased one aware they didn't get a real, genuine Teensy and especially to convince them to complain to the seller for a refund, or start a dispute through their bank or Paypal if the seller won't cooperate. Paypal and virtually all banks will return people's money when presented with evidence the merchant sold a counterfeit product.
These counterfeits do appear to have many problems. They don't respond to the button hold recovery procedure while plugging in the cable. Counterfeits almost certainly are responsible for many of the threads we've seen over the last few months where people had strange uploading issues which don't happen with genuine boards. I need to be much better at making sure people who unwittingly buy these counterfeits can find out they don't have a genuine Teensy.