do microtik routerOS support USB?
no
I agree with Normis to not running M/T ROS on USB because of USB device is not suitable for running powerful Mikrotik RouterOS (except for just for testing purposes.
Pls just using the device/hardware as recommended from Mikrotik. This is very stable system that must be running on stable device(s), such as NAND/Compact Flash or HDD ATA/SATA.
Do you agree?
My main concern is that Compact Flash disks has a limited number of read/write cycles. Is this of any practical consequence for its use as a hard drive replacement, and how many months/years can I expect the CF disk to last before needing replacement? Another concern is that I need a new RouterOS license everytime I must replace a CF disk.
some (all new models) have read buffer integrated so you acctualy read from some kind of fast ram memory 
..
we have yet to see a compact flash that has died running RouterOS. ROS doesn’t do a lot of writes, plus the limitation is far more than you need. Plus, why do you think USB drives don’t have this limit? They are the same
I didn’t said that USB flash drives and Compact Flash disks differ, both are NAND flash memory as you said. My question was how many months/years I can expect the CF disk to last before needing replacement.
we have seen a lot of routers that work fine for many years. if you won’t run webproxy or logs on this drive, it will last for as long as it’s designed for.
Okey, thanks for the answer normis.