To me, this is incredibly exciting news, not only because I happen to love Mateo's potential, as well as his batting stroke, but because of what it implies about the Cardinals' devotion to building the farm system.
For several years now, we've heard the Cards pay lip service to the idea of building from within, rather than through trades and the free agent market, as was the case during the Walt Jocketty era. The only problem was it seemed much of that talk was exactly that: lip service. Even while ostensibly committing to a build from within philosophy, the Cardinals seemed hesitant to make a serious investment, playing it conservatively and making mostly low-dollar choices. Of course, the most famous- or infamous, if you prefer- example was when the Cards passed on Rick Porcello in the 2007 draft, choosing instead to draft Pete Kozma and his at-slot signing bonus over the big-ticket pitcher. Not to revisit the issue in full here, but Kozma is currently a very nice prospect, while Porcello is holding his own as a 20 year old in the Detroit Tiger's major league rotation.
All of that seems to be changing now, though. In the amateur draft this year, the Cardinals took Shelby Miller, the HS fireballer from Texas, with their first-round selection. Miller is expected to be a tough sign, but also has massive upside. Now, whether or not the Cards can get a deal done with Miller remains in question, but the mere fact they were willing to use the pick for a chance to gamble is a clear break from the MO of recent years. (No pun intended.)
Giving the largest bonus in franchise history to an international signee is just another sign they finally get it. You want premium talent, you have to pay for it.
As for Mateo himself, I wrote about him a while back, and my opinion hasn't much changed since. I love the kid's swing; he's got excellent bat speed, good leverage, and outstanding balance. There isn't really enough footage available to say very much about his fielding, but from the few throws you do see, the arm looks good. The soundtrack is still brilliant.
So what are the chances this kid turns into an All-Star? Well, to be frank, not great. Not that there's anything wrong with Mateo; it's simply the nature of amateur scouting. You beat the bushes for talent, and then only a tiny fraction ever turns into something good.
Here's video of Mateo, from the baseball academy run by his representative: