This is a good deal for those who want to test out the experimental Linux beta of Arma 3, as Humble Bundle have unleashed the Humble ARMA 2018 Bundle.
For those who don't remember, Bohemia Interactive teamed up with Virtual Programming back in 2015 to port Arma 3 to Linux and it's currently in an experimental form. It doesn't advertise the support for it on Steam, but it does work quite well. You don't need to opt into anything on Steam, you just download it like any other game.
If you pay $1, you will be able to get Arma Tactics. While this tier does include Arma: Cold War Assault as well, it does not include the Linux version, as Virtual Programming put up the Linux version of that one as a separate game on Steam.
Whereas Arma 3 and the DLC is in the top tier where you pay $15 (around £11.27). This is probably the tier most of you will be interested in and it's not a bad deal really considering it's currently $39.99 on Steam directly.
Check out the Humble ARMA 2018 Bundle now if you wish.