Here's my quick impression.
The CAST are the best caps I've heard so far. But are they worth the price, probably not for everyone.
Over the MR, they offer a little more transparency and better tonality. Imaging, soundstage, dynamics, are similar with both caps. Must be something to do with their anti-resonance designs.
I've experimented with MR, VSF, and CAST in three different speakers. My Tannoy Saturns have perfect synergy with MR's in the HF circuit, I have no desire to try anything else in them. My Tannoy HPD-385A's use three caps in the HF circuit, replacing all three of them with MR's gave a little sheen, I replaced one of the caps(the only in series) with a VSF and found synergy. Since these are in a secondary rig, I couldn't imagine fronting for a CAST in that position. Now for my dedicated two channel rig, I use custom speakers consisting of Seas Magnesium drivers and a Scan Speak Air Circ tweeter. I've tried a few different caps in them, including Mundorf S/O, VSF's, and MR's. MR's worked the best overall in them, but I still preferred Duelund's tonality in that rig. I then ordered a pair of CAST's for those speakers. While waiting for them, I ordered a pair of small VSF's to parallel with a pair of MR's. Paralleling the two gave me most of what I'm looking for, but still wasn't perfect. I like to use a single cap in the HF circuit whenever possible. I found that paralleling or "bypassing" caps in the HF circuit usually leads to some signal degradation, I haven't noticed this in MP or LP circuits though. Finally the CASTs arrived(ahead of time too!). As I mentioned before, they have the same large soundstage, and precise imaging as the MR's, but with a more natural tonality and little more detail without harshness. If I had unlimited funds would I buy these for all of my speakers in every position...no, because I still do prefer MR's in some speakers. I still wouldn't mind having another pair or two though.