It’s a pretty clever solution to their power needs and it beats the hell out of the alligator clip hack. If it were my house I would let them use this, the worst that could happen is their equipment and cord past the 20A twist lock is not protected, and hopefully the motor would have some overload protection.
Sure some contractors have generators, but which bid did you select the high guy with then generator, or the low guy with the home made cord adapter?
