This small and lightweight UBEC features a high efficiency switching mode BEC, providing better heat dissipation when compared to linear voltage regulation. The shielded PCB design and output EMF coil provide a stable, low noise voltage output. The HKU5 also features built-in reverse polarity protection.
Input voltage is in range (from 2 to 5s) so 3 or 4s is OK.
Output voltage is 5v DC so this match your requirement 4.8-6v.
The only open question is your current (or power consumption) requirements .
If required current is less then 5 amp (or in terms of power less then 25 Watt),
then yes it's OK for use with your headlights.
If your camera has good power filter then yes. The problem is that's this is SWITCHING BEC which provide not well fitered power with HF frequency ripples which path-through to video.
For camera, I'd recommend to use LINEAR BEC ... and hardly you need more then 1A ... so linear one is preferable for camera feeding
Most ESCs with BEC has linear 5v bec 1A build-in... So if you have ESC, then you can use ESC bec output for feeding your FPV camera... On multicopters you always have unused ubecs in escs...why not to use what you already have... If not then ....single chip LM7805 and 33-100uF capacitor will do the same...
Unfortunately HK do not offer separate linear BECs, as well as most other suppliers too.
The best practise is to connect all power connections at one point (star type as opposite to tree type wiring). So connecting to power distribution board is a good place.. Other thought. This bec is low current .. so you do not need 3.5mm bullets which is ok up to 30-40A ... you may smaller ones like 2mm to save weight.
Purchased three of these for ignition voltage regulator duty in my large scale gas planes, when paired up with the turnigy 2100 Lipo receiver pack, you can run an engine all day versus the 4 cell NiMH packs. Working great in my planes, the 3A version works great too, but is a little longer and slightly heavier, but cost less. Next order, I will order more for spares for future projects.