Didnít that Ferengi guy with the vendetta against Picard (Damon Bok?) also use some sort of ultra-long distance "subspace transporter" beaming technology too?
Though Scotty's "transwarp beaming" didn't just involve super long-distance beaming, but also beaming to a starship moving at warp speed (and potentially from one ship at warp to another ship at warp...)
I think subspace beaming was done using a tranceiver at the other end and then by piggy-backing on the signal on the way back. It's still not clear how it differs from conventional transporting but it must be a less safe version or the Federation would use it as standard.
I don't have a major issue linking local tranceivers to chain-beam a signal to effectively double the distance but given the rate at which information leaks on these transports because of the energy needed to maintain a pattern (Scotty's genius took pretty much all the shuttle's power to prevent the patterns from degrading I think) if a signal is being sent through subspace it should be a real bitch to maintain for long. And subspace travel isn't instantaneous. It can take hours for messages going via several relays to reach Starfleet Command. Nothing should be surviving that (I realise that this is an issue from the recent comics rather than the movie).
Beaming inanimate objects with not complex working parts should be fine though. And with your anti-matter bomb, it doesn't matter if your signal degrades over long distances since you only need your magnetic shielding to last while you dematerialise. If it explodes immediately on rematerialisation, so much the better.
It's also worth noting that transporter pads can divert a signal and can deactivate weapons as part of the standard failsafe. Presumably if the transport is rerouted to a pad, your own systems could simply not re-materialise the anti-matter, although exactly how it could tell that in time is anybody's guess.