I tried to connect a HannsG HT225HPB 21.5'' touchscreen or an Elo ET1502L to my Raspberry Pi 3. Both connect via HDMI and USB for touch.
Both seem to work at first glance but are not really usable. If i touch a point on the screen the position of the touch is recognized just fine but I can't klick. It seems completely random how my touch is recognized. Sometimes its a rightclick, sometimes a mouse drag, sometimes a leftclick sometimes it just moves the cursor.
These problmes occur with raspian jessie and ubuntu mate for the pi but both screens work just fine on a ubuntu desktop pc. I assume it's a problem with kernel drivers but i can't figure out a way to fix it.