Not GP, but presumably the point is that must be using USB, so the only point is convenience of form factor/you already have the card/whatever - it can't be faster (if anything the converter's going to slow it down) than using a USB storage device.
Honey, *everything* gets converted somewhere, somehow. That's what all those components inside our computers do.
MicroSD gets converted from SDIO. USB flash drives get converted from their proprietary NAND/Microcontroller config. Might as well be saying "you're converting from electricity to bits, isn't that extremely wasteful?"
Just ran a benchmark in Gnome Disks. 362MB/sec read, 313MB/sec write.
But given that there is absolutely no other way for me to connect this flash drive to my Pi4 without defeating the point (replacing both the entire Pi4 and Case), I would say it seems to be doing fine. Especially compared to something with generally equivalent durability like, say, a hard drive over USB 3.
