One thing is check the response time. Some take 1/400th of a second to respond, others can be 1/25,000th.
1/400th of a second may sound "fast enough", but consider a camera flash is typically 1/1000th of a second (can range from 50us to 3ms). You know how long you see spots with a camera flash.
Weldequip: how fast is the one you offer? Scanned the tread and did not see that mentioned.
That is what my "cheapie" is,( 1/25,000 sec). It is amazing, you don't even notice it switching. Set at about #9.5 works great.0.00004 seconds
weldequip