Both of these are fun, and theyre an interesting combination for sure
The reflexive triggered ability will trigger any time you lose control of that Equipment this turn, whether it's because the "until end of turn" duration ended or because someone else gained control of the Equipment with another effect
"Mill" is a colloquial term that originates from the card Millstone, used here to mean "putting the top cards of a player's library into his or her graveyard." For example, you could say, "In the finals of the Pro Tour Qualifier, Herbert cast Tome Scour to mill away my final five cards, dashing my chances of playing on the Pro Tour." There are many players who will play with Tome Scour in their decks
Urabrask, the red praetor, doesn't cooperate with the others, so he wasn't involved in the process
Even the least expensive two can be had for less than $1, and can be a Crucible of Worlds or Brokers Ascendancy minus the loyalty counters, I love the options on these