So last night I fitted one of these. It was £17.99 off Amazon, has good reviews and was easy to fit, even for a mechanical retard for myself! I did manage to break a fuel hose removing the tank though
I can now run a sat nav and change my phone and my kindle at the same time! Result!
The one I got has no switch, I guess there is a transformer in so presumably if I connect it straight to the battery it will drain it even if nothing is connected??
A socket will consume power while it is connected. However, the amount of power is very small. When there are no devices plugged in the power drawn will probably be so small that it will not be a problem if the motorcycle is in regular use. I have one on mine that does not have a switch and it does not kill the battery.