Absolutely great.
Survival is a problem even for beefy characters, Tetsuo is a 2 - in - 1 combo that tanks a couple hits and then hands you a gun with which you can now avenge him.
An ally card with 2 and 2 life is worth 1 resource already (see: allies) and Tetsuo backs that up with a slightly better form of Prepared for the Worst as well. At 3 resources he's a tiny bit hard to fit sometimes but you'll never regret taking the space and time to get him into a deck and onto the table.
Absolutely check him out if you're going for a big gun build.