Thatcher will play 2015 as a 33 year old. He is the veteran of an 8 year career, in which he has thrown 238 innings, with a career ERA of 3.40 and a career FIP of 3.21. He has allowed nearly a hit per inning (8.7/9), has walked a few (3.0/9) but also struck out a few (9.2/9). His best strikeout seasons are 2009, 2010 and 2012, where he struck out equal to or more than 11 per nine innings. In the last two seasons, his K/9 rates have been 8.2 and 8.0, so he is still capable of a good number of strikeouts.
Speaking of the last two seasons, he has been traded twice mid-season and on each occasion, has done worse after the trade. In 2013, Thatcher went from San Diego to Arizona, and in 2014 he went from Arizona to Anaheim. He injured himself shortly after the second trade, and struggled plenty, so his most recent performance is potentially of concern, if that is how you want to look at it. But most sprained ankles recover within an offseason, so chances are that he will hit camp healthy, and be ready to go.
This signing adds another legitimate ML player on a low-risk deal which is solid insurance for the Astros. I would think that two of Thatcher, Tony Sipp and Kevin Chapman will emerge to put the Astros in a good LH relief position for 2015. Also lurking in the background of the 40-man roster is the undersized lefty starter with a solid strikeout rate, Luis Cruz, who may be in the mix as well. Despite a recent roster crunch, he has maintained his place on the 40-man, so there is obviously some plan for him going forward. This may involve the 'pen in 2015 - who knows. Cruz... ahem, was invited to Spring Training by virtue of his 40-man roster spot - thanks, commentator - so he may be a candidate for a role in the ML club from the start of the season.
The only other interesting aspect of this trade is the ongoing resurrection of the 2011 San Diego 'pen, which also contained Chad Qualls, Luke Gregerson, Sam Deduno and Pat Neshek. The 2011 Padres 'pen also contained recent ex-Stros Wade LeBlanc and Anthony Bass, and ex-Stro from ages ago, Jeff Fulchino. Is the NL West the only place the Astros scouted in 2011??
Thatcher and A.J. Hinch know each other from San Deigo, as well. Fascinating that pretty much every reliever the Astros have added this season has played in either Arizona or San Diego in the last 4 years. Even if Hinch is fired now - which isn't going to happen short of some grossly inappropriate behaviour or significant criminal court charges - he has left an indelible mark on the 2015 Astros by virtue of his recruiting. Which is possibly a sign of respect for the man.