Dual injection points to EoP / powerline

Apologies if a dumb question but I have a spare D-Link EoP unit that I could use as a second "injector" ...... providing it doesn't screw up the already tempremental powerline setup.

I use Cat 6 reticulation wherever I can but of necessity have a number of WAPs running off powerline and wondered if dual injection was of benefit or dis-benefit or downright counter-productive?

Thanks & regards,