In general modern studio flash is very reliable. I have on occasion had cheap flash heads bust into flames after a heavy session of use but in general there pretty reliable.
The main problem with cheap flash heads is consistent colour temperature. Having a drift in colour temperature is very difficult to overcome as you have to then edit and correct every shot manually. During each scene during the shoot I take a reference shot with a white balance card to correct for colour. With the better flash heads having consistent colour temperature I can correct the white balance on the reference shot and then sync that colour temperature across all photographs of that scene.
This last weekend though I had an odd problem. As you can see in the shot above, only half the frame is exposed, this is generally caused by using a shutter speed too high.
I was using a radio trigger but no matter what speed I set I had this intermittent sync problem. I tried several triggers and it only stopped when I switched from wireless to infrared. Not a problem I had seen before and I hope not to have again.