I know that these new Delkin CFAST Cards are not officially certified by BlackMagic Design to work with the URSA cameras, but I wanted to know to what extent it would work. I'm sure a lot of you shooting with the URSA want to know the same, so I'm throwing up this post. Without getting too technical or running any scientific tests, my experience is that it's probably stable when used at HD resolution (1080), lower framerates, and anything less than ProRes HQ.
So while it can work, I don't think it works well enough to consider this your primary storage. The super long delay of the DELKIN CFast Cards during formatting makes me a bit weary as well. If you're really hard up on a budget you can try those CFAST to SSD Adapters which give you best bang for the buck.
But those external SSD Adapters get in the way sometimes when you're trying to fly on a gimbal, or run a compact rig. Eventually you'll find you need at least one good set of CFAST Cards. At the moment the most reliable, 'officially supported', and least expensive CFAST Media for the URSA Mini is the Transcend Cards (found here).
Transcend CFAST Cards for Ursa Mini
Slavik
Another option for cheaper Cfast 2.0 cards is the Transcend CFX600. They're about $160 for 256gb. I bought 4 of them from CDW and have been using them exclusively on my C300 Mark II in all resolutions and frame rates, bitrates and slowmotion, and they've been flawless. They're not officially approved like the CFX650 cards, but I think the issue may have been some sort of error in the manufacturing process that reversed the label so it appears upside down - you have to load the cards opposite the way you load other Cfast cards.
I contacted Transcend to ask if they're discontinuing the cards, since they're not available in major retailers like B&H, and they're constantly backordered at CDW and smaller retailers. Transcend told me that they're not discontinued, and in fact they're having a hard time meeting the demand for them.
The cards have also been used in my XC10 regularly. I do have a couple Ursa Minis around (4k, not 4.6k) that I can do a quick test with, if anyone is interested. But I don't use the cameras often and wouldn't be able to say much about long term reliability.