These would be nice if you have a bunch of sd cards laying around though not very fast unless...

I can't find one of these that support UHC-II let alone UHC-I but if they could support it considering the fastest sd cards are around 250-300MB/s, though expensive it would still be cheaper and more power efficient than the top storage enterprise solutions out there currently. The only issue being they would be in a raid without parity and the max bandwidth of sata3 is only about 750MB/s. I know it's not a very practical idea, but still interesting imo. Anyone have experience with these devices?

assuming this talks about sd card to sata readers.

Most people dont buy top of the line devices because they tend to be expensive for no reason. A standard ssd capable of 500MB/s is fast enough for most things. At this point in time if someone needed faster storage they got 3 option. put ssd's in raid, m.2(for supported mobos), and Pcie ssds. with each option increasing in relative price per unit but also increases in max speed.

using sd cards that reach the max speeds would be expensive

I've had the thought before. It'd be nice to put the old cards to use if the adapter were cheap enough, especially if you had some old junker whose drive you needed to replace and it wasn't worth spending much on.
Blazinf fast UFS cards 

So what about the same idea but with these UFS storage cards? Maybe to a m.2 interface or pci-e?

why not integrate ufs cards to sata if the adapters are made?