Yeh mate, it can save your life on Survival
Your third follower will follow you to Nuka World and anywhere in the Commonwealth including the Glowing Sea because Travis Miles doesn't give two fucks about radiation
Basically, think of DJ Travis as your Brynjolf
He's hip, he's fashionable, and early on, he's totally not available as a follower except for That One Time
...so when you FINALLY get him to accompany you on a quest, you just say Fuck It, turn away from the cave and abandon said quest entirely, hauling his ass over land and sea for nineteen years
Similarly with Travis, if you sleep for a day or so at the Dugout Inn (Diamond City) -- which is pretty f*cking common early in Survival mode when a house isn't an option -- you unlock the start of the "Confidence Man" quest:
I was royally bummed to receive the quest, since I've always sided with the Dan-Harmonesque radio stumblings over confidence, because Fuck confidence, what is this, the non-apocalypse? The man is allowed to be scared as balls. Fuck you, Vadim
To get DJ Travis watching your back with a follower or without, you complete Confidence Man until it reaches the part of the quest where you "Meet Travis at Beantown Brewery"
Travel to the exterior of Beantown Brewery where you will give Travis a small pep talk about going in there and murdering multiple humans in cold blood.
Once Travis agrees to follow you, DO NOT ENTER THE BREWERY.
Just turn around and go literally everywhere BUT Beantown
Beantown is off limits for you. You are officially banished
Travis is now your homie for life
As far as I can tell the game doesn't recognize Travis as a companion in any official sense of the word, so your Lone Wanderer perks apply if he's the only follower you have.
Travis may get 'downed' repeatedly on survival mode, especially early on with his starting pipe pistol, but don't give up on him yet.
He requires ZERO stimpacks, and revives himself in the middle of combat like a goddamned war machine
If your Travis is 'downed' from high DAM enemies (deathclaws slapping him down, Sentry Bots, bosses, etc) and you want him revived immediately, just hide anywhere to reduce your detection level. As your detection level goes down, Travis jumps to his feet and starts murdering everything in sight. This is CRITICALLY useful when your follower is downed near enemies, and can't be reached. Travis will simply hop to his feet no matter how many enemies surround him, and start blasting away until downed again
One more note about XP: like regular followers, any enemy that is killed by Travis will not net you experience unless you personally do damage to that enemy. If you want credit for killing advanced enemies, you have to land some shots yourself before running away and hiding behind a wall while Travis and your follower massacre everyone. On Survival mode, whittling away at skull-marked enemies is the only strategy sometimes, so get used to hiding from shit
*Edit:
I almost forgot the most important part:
When Travis is your third follower he can take some friendly fire (the occasional grenade, missile splash damage, molotov, etc) but be SUPER careful around him. If you piss off Travis while he is glitched into following you he will become your worst nightmare, following you everywhere you go, hunting you down, only getting downed temporarily. Travis will Fuck You Right Up if you piss him off, because you are essentially handcuffed to the man, hostile or not, and he cannot die while following you (marked essential.) Don't even ATTEMPT a pickpocket unless you're ready to reload a save point, because failed pickpockets will launch him into a murderous rage that will never stop.
Travis never forgives, and he never forgets
Oh, and if you're used to stealing items in Diamond City while hidden, steal everything from Diamond City you need before joining Travis. I forgot that he remains a citizen of Diamond City while following you, and so
stealing anything while completely hidden in Diamond City will be noticed by Travis, because he's always two feet away and staring at you constantly
If you absolutely HAVE to steal something in view of Travis in Diamond City, make sure you close a door or find a barrier to his sightline. Or he
will murder the fuck out of you
If you need to dismiss Travis, travel to Beantown and rescue Vadim. This will make Travis unavailable as a third follower forever however, so I recommend doing everything you need to do solo first, then taking Travis along for the ride permanently
**EDIT EDIT**
Also one quick note about stealth detection with Travis:
Travis can see you almost constantly
Because he is not technically considered a follower, this will mess with your stealth status, and it will often read "DETECTED" because Travis is always watching you
Even if your status reads "DETECTED" from Travis' point of view, you will still be able to hide from enemies and rack up stealth bonuses. Just ignore the stealth status level until it displays red stealth statuses like CAUTION and DANGER, because "detected" won't affect you, unless you're stealing something in Diamond City, in which case Travis is about to MURDER you (see above)
I remember reading something similar about the guy who beat F4 Survival on a single life, but was almost undone by pissing off Preston Garvey as a glitched third follower. You don't want to piss off your third follower, because there's no talking to them. There's also no killing them. There is only endless war
