I have bought this touch screen.
It looks and works great. I wanted to play round making a simple Kivy app with buttons that turn on/off LEDs and relays. But it seems that when the screen is connected (via HDMI and USB, screen has its own PSU), the GPIO pins don't work. The 5V and 3.3V pins work fine and a LED lights up when connected, but switching other pins doesn't work. Nothing happens.
Using this simple script to test:
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
while True:
print "ON"
GPIO.output(17, True)
time.sleep(1)
GPIO.output(17, False)
time.sleep(1)