The first time I heard about them, was due to the great Pepe Mujica (he was a member), but never searched about them, until I found this book in a second hand fair several years after. I remembered about it and decided to blindly buy it.
It's a great book about the political/social economic environment in Uruguay, during the first half of the 20th century, and how the Tupamaros rised against the capitalist/imperialist forces.
I would say it's undoubtedly not outdated, because the fight against reactionary forces is a universal one and we definitely get an idea of a possible modus operandi.
Note: I've read a portuguese version from the early 70s. But I couldn't find it here, in Goodreads
Note 2: If anyone is interested in the book, hit me up. I can borrow it.