The Blackmagic HDMI to SDI converter works fairly well, with some caveats:

1) You must update the firmware to the most current release. Prior to the firmware update, the image from the 5D Mark II (with or without Magic Lantern) would display a black line across the screen, when recording to CF card. The recording was fine, but the black line caused clients (and me) to freak out at first. The firmware update appears to fix this.

2) Despite the product being labeled as having a "+12 Volt" input, it DOES NOT WORK WITH ANTON BAUER DIONIC 90's. Yes, you read that right. Since the voltage of a fully charged Dionic 90 is 16.5V, the Blackmagic simply does not turn on. When the Dionic is nearly drained, with a voltage under 15V, the Blackmagic will power on. But, this makes it almost completely useless as a product you are using with a field monitor remotely. Interestingly enough, it works just fine with a 5V power supply, so under voltage is Ok.

If you need to power it in the field, it works just great with lead acid 12V batteries (which are 13.5V max, usually). So far that has been my solution to using this product in the field with Panasonic 8" and 17" monitors. Just keep this in mind before buying one.

Interesting info.
Thanks!

I have been using the Blackmagic box with success powering via d-tap from an Anton Bauer Dionic 90. The solution is to use a simple voltage regulator (like this one from Radio Shack (http://www.radioshack.com/product/index.jsp?productId=2062600) inline in your power cable. It limits the outgoing voltage to 12v. It does get a bit hot but so far it has performed fine. Down the road I will have more robust voltage regulation set up for it but for the time being, no problems.

My preference is to use the box at the camera and then link to the monitor via HD-SDI cable (or better yet, Camwave) rather than the delicate and length-challenged HDMI. This obviously is a challenge in terms of mounting and power, but I'm working hard on a complete solution now via custom machining and Redrock parts.