If he's fit, he'll add a lot to the midfield. Age still on his side at 30 going on 31.
Checking out his international appearances for Costa Rica, more impressive than I realised -35 apps, 7 goals
The stats for him on Wikipedia are very incomplete - rather check out his page on FIFA.com here:
http://www.fifa.com/worldfootball/statisticsandrecords/players/player=182587/index.html
including: 2001 FIFA U-20 World Cup, Argentina (all four games incl. vs. Netherlands, Ethiopia, Ecuador and Czechs in the round of 16)
2004 Athens Olympic Games (all four games vs. Morocco, Iraq, Portugal and Argentina in the quarter-final)
2006 FIFA World Cup, Germany (2 apps in finals vs. Poland & Ecuador))World Cup qualifying: 9 apps in 2006 qualifying incl. against Mexico, USA, Trinidad, Canada, Honduras, Panama, Guatamala
(Costa Rica qualified directly as third place side in CONCACAF behind USA, & Mexico);
4 apps in 2010 qualifying vs. Mexico, USA, Honduras, El Salvador (called-up for the final round of qualifying & Costa Rica made it to play-off vs. Uruguay as fourth team in CONCACAF )
International goals include in two World Cup qualifiers against the USA 2006, and a winner against France in a friendly in 2010.
His most recent appearances for Costa Rica were in three friendlies in 2011.
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Apparently the Aussie government are so down on people from places like Costa Rica that they wouldn't renew Carlos' visa once Melbourne Victory opted not to renew his contract last year (he was in a "no current job, no right to stay" kind of situation on his visa) so he couldn't even stay to negotiate a deal with other interested A-League clubs...Also the Victory pissed him around in contract negotiations. See here:
http://www.foxsports.com.au/football/a-league/carlos-hernandez-labels-melbourne-victorys-treatment-unprofessional-in-an-interview-with-simon-hill/story-e6frf4gl-1226402893872