If I have rune of spellbreaking on multiple rune smiths can I use it once on each of them? It says one use only, does that mean one use only on that character or for the entire army?
I believe this is intended to mean "one use only" per rune item which has the rune.
I cannot find anywhere this is stated outright in the 8th ed rules, but this is how such items have always been played, at least in my personal and tournament experience.
It would be odd for them to let you take more than one and then limit you to only using one of the Runes you paid for.
The term has been used in numerous previous editions, and in those cases you could buy multiple "one use only" Dispel Scrolls etc in your army and each scroll could be used "once", not one scroll despite how many you had.