Are these bad? Mastery is a C+ in TDM. I feel like they look decent to stop an early threat without being overly disruptive to an Eldrazi Titan.
I've recently seen some very new Cubers put Ringing Strike Mastery alongside what would otherwise be considered Vintage-level removal, and I've come to think of them as very savvy. It's not too far off from Swift Reconfiguration besides the flash, which is a pretty big difference, sure, but that's not an unreasonable downgrade to get on a blue version of creature removal. I agree @ravnic that it's a C-level card at best still, but the fact that it can be a C both in its retail draft environment and in pretty much any Cube you throw it in is both fascinating and true.
The biggest issue with Ringing Strike Mastery is the same issue with Swift Reconfiguration -- the card still has its abilities in the meantime, too. While ETB and attack triggers are the most pernicious parts of most creatures in modern magic, there's little value in using a card just to lock down someone's Suki, Courageous Rescuer.
I personally prefer Sleep Magic, which makes the "out" quite a bit harder, or the Witness Protection/Unable to Scream duo. I don't like the "face-up" text of Unable to Scream, but I do prefer it to Witness Protection otherwise.
I think the cards get much more meaningful at 2 mana, but then you have to ask yourself why you really need these effects in blue, instead of asking your blue players to use other colors if they want to do a creature removal. That said, I think these cards are all pretty good and Cubeable/scale to the environment well in most lists short of Vintage power-level:
(I'd never Cube Fresh Start for a similar reason many others would never Cube one of my favorite UB cards, Kylie Minogue)
Also Bubble Snare is cool, I played that card for a good few months IIRC.
is the original "once per turn" clause 