If one is lucky enough to come across some Chameleon armor, Stealth Boys become one more item to trade for good caps.
Stealth Boys are better used preventively (ie avoid combat) rather than reactionary (ie escape combat). If you are in Caution, approaching a room full of enemies, or coming up on a hallways full of turrets; use the SB before actually entering into a firefight.
They're not very effective, otherwise.
The only issue I have with the Stealth Boy is the time it lasts. Feels much too short compared to previous Fallout games.
I'm more concerned about the lack of chinese stealth suits. What the [censored] happened to those babies?
I used them in FNV on occasion. But OP does have a point. It seems as if they hit you just fine when using a stealth boy. Even when in stealth mode.
Stealth boys help you avoid detection in brightly lit areas. If someone is shooting at you, it would be a safe assumption that you have gone past the trying to not be seen phase and are now firmly in the kill or be killed phase.
I pressed Q all the time during the final talk then set up an series of headshots, If VAT is used before he enter stealth it will still hit.
Stealthboy makes you very stealty, it will not help you much if discovered but is very effective if undetected.
I only used it multiple times under the mission to blow up the airship as I did not want to face lots of enemies in power armor.
I could sneak past enemies in stairs so its very effective.
I don't however see much use of it in normal gameplay, in TES I use invisibility plenty as you do plenty of missions where you have to be undetected to steal or similar where you can not kill your way in.
In Fallout 4 stealth is an way to avoid enemies to rush you.