I know this is a cheap solution but if you want real reliability invest in a pair of HDMI to SDI and SDI to HDMI convertors (you may well only need one of these as you can use the SDI ins or AUX SDI outs on your atem (BM even make battery powered convertors so you dont need power on your camera). Long HDMI may work ok but the cables are not reliable or flexible, you may well get dropouts in a show that you did not get in tests. In the end if you want your picture to be solid and good all the time use SDI for long runs, you can carry a whole stack of short HDMI cables for the last links, the HDMI connectors do not lock and wear out fast with the weight of a heavy cable- you have a good chance at damaging the HDMI output on your device (I am speaking from experience, I had to get the connector replaced on a camera and for the cost of this repair I could have bought the convertor). BM will not support you with problems with long cables. I understand the temptation, the initial cost is low and I fell for the same temptation but speaking from experience dont do it- you can actually save money in the long run by doing it properly now- and these little boxes can come in very handy for other applications. Also the directional nature of the cable means you now have another place for things to go wrong in setup, imagine you get an assistant to help setup and then you have to stop and re-do you very long cable run.
So not really the answer to your question, no I have not tried them but stay away from this kind of stuff if you can.
Fred