http://joetedesco.org/wrong.jpg
The installation shown in the image is not the intended application or listing recognized by Underwriters Laboratories (UL) and VIOLATES 110.3(B).
As I interpret this picture there is a malleable iron squeeze type connector securing the flexible metal conduit, and on the other end the steel set screw connector is assembled to EMT.
Both connectors are joined to a coupling with the connectors locknuts made up tight (?) to the coupling.
First, a connector cannot be used as a coupling unless so listed.
Second, connectors have not been UL tested for resistance or ability to carry potential ground fault current when assembled to a coupling.
Third, the threads of the connectors may not match those of the coupling raising the risk of connector pulling out of the coupling.
Fourth, there is no assurance that the locknut(s) will not loosen.
A better choice for this installation would have been to use couplings designed and listed for the application.
Fitting manufacturers such as O/Z-Gedney offer such a coupling for trade sizes 1/2" EMT - 3/8" FMC up to 2" EMT - 2" FMC; Bridgeport Fittings has sizes 1/2" EMT - 3/8" FMC up to 1"EMT - 1" FMC.
Here’s a reply from UL:
UL has not specifically tested the rigid metal coupling to flex to EMT fittings as used in your picture so looking in the UL White Book and the guide card info would not provide you with anything you could use for the evaluation. However, the flex would normally have an equipment grounding conductor installed in the raceway so ground continuity would then not be an issue. Bonding also does not seem to be an issue since the flex connector also uses the locknut to tighten to the coupling with the ability to keep the flex connector tight to the coupling. This is done in many parts of the country without the installation being an issue.
PS: I have been advised that the NECA Publications for Qualified Persons shows this method.