If you are playing a sniper, for sure get it. It's a much better gun than the starting abomination. If you are playing a gunslinger, get 2 of them, so you can dual shoot, or get 2 of some other pistol. It is not as much of an issue.
In CK, aside from Predator Drones and Horizon Drones (neither of which you meet in the tunnels) __every__ monster you meet has mental points that are less than or equal to their physical points. And many monsters have many more physical ones. Thus mental damage kills them faster. Try taking out a red hatted boss with a blasta gun, and then a regular lightfire .... with mental damage, he dies a lot faster.
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Btw, in the mission stealing from the tunnel stores (and blowing up the cache afterwards) ... you might want to have a marker in the map to show where you are supposed to place the bomb. I didn't figure that one out straight away and had a few more encounters while I hunted for the bomb point.