Homeplugs va extension leads ??

Hi
I've just bought a pair of 200MB homeplugs from TP-Link.

The quick setup guide shows not to connect using extension leads..
Will this cause any issue ??

Where I plan to use them, both ends are on extension leads. I've plugged them in and they are working.. but are they safe on the extension leads ?

Also are they encrypted by default ??

Thanks