I have a Nitecore P12 that does indeed have the SOS and beacon modes and they are actually fairly easy to access as well as two Zebralight headlamps that also have that feature; on them it is somewhat more tricky to activate. I can't say that I bought either of them for that feature specifically. I like them because they have variable light levels, long run times, and seem to be quite sturdy and dependable.

My Zebralight 502 headlamp would probably be my choice for a lamp to carry where weight was really critical. Signalling at night, if the option is available, I would probably prefer a signal fire, which would tend to conserve my batteries. I would also consider carrying my Zebralight that runs on an 18650 battery - the slight additional weight is repaid in significantly longer run time, especially at lower light levels.

The SOS/beacon feature is fairly low on my list of significant criteria in evaluating and purchasing a light.