This is what I tell most of our clients when this question comes up.
The blackmagic cards do work, but they are pretty much just I/O and they’ll get you through the project, but unless your system is perfect (and you can keep it perfect) it’s not something you will want to build a permanent workflow around.
The Aja cards are built for quality, you may not get the most realtime functionality, but the hardware and software were designed for a very professional workflow from ingest to delivery.
Lastly (and most expensive )the Matrox Axio was designed for realtime functionality, if you need your project done and done fast this card set has all the realtime effects and transition you’ll want and many you’ll never use. You will be limited to single link and a few other short comings.
All in all, you have a good amount of choices to find the workflow that fits into your budget as well as fits with the equipment you already have. My opinion is (and I build everything) is the AJA cards are the best all around, but it all depends on what your shooting and how your delivering. as well as how much cash you are willing to spend 🙂
Cutter Stevens
Technical Director
DV411