So the book says Xexto get an additional free maneuver due to their 4 arms. But they still can't do more than 2 maneuvers per turn. How is this beneficial? Trying to figure out how something like this would work. Was debating making a villain similar to Pong Krell to throw at my group, and was going to try the 4 arms approach for 2-handed weapons.

Thanks in advance.

Because of action economy it bring. Normally you get 1 action and 1 maneuver. In combat, it would be like many with the "Aim -> Shoot". You can get 2 stress to add another maneuver, such as moving into position.

Now, with the Xexto, you can perform that 2nd maneuver without getting two stress in the process........

Doesn't it mean they don't have to spend strain to perform their second maneuver?

I'd say the second maneuver is very useful. In my campaign the players burn up strain getting extra maneuvers all the time.

I can see this happening a lot:

M: Aim

M: Aim

A: Attack with two boost dice

Seems a significant but not overwhelming advantage.

Since my players ALWAYS pay either two strain or two Advantage for a second manoeuvre in every turn, I have no problem seeing how this ability would be useful.

Pretty much everyone above nailed it; it doesn't cost strain to get a second Maneuver.

Here's another benefit, there's a Crit result out there that prevents the character from voluntarily spending strain (Winded?). That means such an injured character couldn't spend strain to get a second Maneuver until the end of the encounter. Xexto are effectively immune to that aspect of the critical injury..