No, he's not a sure thing. Speaking of which, what exactly is one "sure" of with Masterson? League average SP? Alert the press. Above average RP who might need to avoid good LHH? Shiver me timbers.
Look, I think Masterson is better than that, but there's no surety of this belief. What's more, he's expendable. They have one of the best 'pens in the league without him in it. They can compete this year without Masterson in the BP. They have more than enough starters to fill the 5 rotation spots once Matsuzaka returns (and they need to find a way to get Buchholz in there - then Smoltz is around the corner). It's wasteful to have an expendable player replace the mop-up guy, Hunter Jones, in the bullpen when you could "expend" him for a guy who, while no sure thing, has shown siginificant potential for being an above average offensive catcher while being excellent defensively, especially when you have no catchers coming through the pipeline at the moment and your starter is one month away from pulling his annual corpse impersonation.
I don't care if trading Masterson for Teagarden is 1 for 1 in terms of trade value. If that's what they want, and I'm not saying it is, you do the deal. You do it if it's Bowden too. You don't need both to move forward, but you need options at catcher. You are better, IMO, with Teagarden in the mix and one of them than you are with both of them, for the simple reason that both of them aren't likely to get enough opportunity to be significant contributors given the current roster. Moving on to subsequent years, it will be easier to replace an above average RP or 5th SP than it will be to find a catcher.