I am using ALIX boards for hotspots with UM, because of Flash-Disk and easy set-up. Is a RB411AR (definitely cheaper than ALIX) good enough to run hotspot + UM ?
I never used RouterBoards, so the stupid qustion: Is the NAND-storage of the RB411AR equivalent to a flash-disk ?

No

No

To which of my 2 questions did you answer ?
And, please, be more specific. Can the NAND-storage used as a "data-storage" for UM to store its DB, and to store all the files for the hotspot ?

whats does it mean by UM ???

and the hotspot depdns how much traffic and customer can hang your equipmnt.

UM = User Manager

The NAND is build in a similar way as a flash disk, it uses a chip for storage. It's mainly meant to be a CPE device, but I suppose that you can also use it to run a small Hotspot with UM. The CPU and Memory are enough.

UM = User Manager

The NAND is build in a similar way as a flash disk, it uses a chip for storage. It's mainly meant to be a CPE device, but I suppose that you can also use it to run a small Hotspot with UM. The CPU and Memory are enough.

How small? 5-10 users?

More like around 50. It only has one wireless card and one AP can only take as much (802.11 limitations not this particular RB).