@Katus 

Hey

Hpoefully some answers for you

My questions are how much durable are they? I bought them in 2014/2015

Honestly, and this is just my opinion 3-4 years is the expectation for these.  Ive never worked out why but after that time range they start to cause issues, be that disconnects.. syncing.. slowness etc and no matter what you do it never gets better.  The 500mbps model you have is the AV1 (first generation) standard and its common for age related problems.. the AV2 seem better (so far anyways)

and why the product should be plugged into a single socket and not in a multi-socket?

Its down to traffic, draw on the line

The more power you pull from a line the noiser it gets and therefore the speed will deteriate.  Ideally they should be on their own connection however..

1. Passthrough plugs work cause the interference is after the plug, if that makes sense

2. Normal multi socket (no trip or surge protection) will work, but noise/load from other devices does greatly affect the plugs on these.  Expect ~50% loss

3. Surge Protected or Trip base multi leads detect the extra noise/static that these plugs use to transmit and 'filter' it out.. usually it renders the plugs useless and thats what they mean by "no multi leads"

Thats the very over simplified version, hopefully makes sense! :)

@Katus Ok, thank you very much, I think I'm a little bit more expert on the argument. Now I've one powerline plugged into a multisocket and it is alone exept for the fact that the multisocket is plugged into multisocket with the main router and another plug, and one powerline that is in a multisocket with a pellet stove. I think that the first one is influenced by the router and the other plug, because data comes from the multisocket which has the powerline adapter and goes to the multisocket plugged into the wall, even if the powerline is "alone" in the multisocket. Am I right?

P.S. now it seems that my powerline adapters are fine and it isn't necessary to substitute them, but I'll see because I'm not sure

@Katus 

Yes you would be correct, the draw of power from the Router and the other Plug would 'dirty' the plugs signal and reduce the speed on you.  If you have to use this setup I found it was best the plug was the first device on the multisocket (nearest to the cable), for some reason it seemed marginally faster there, still not ideal however.

In theory if the homeplug was alone on the mutigang it shouldnt affect it, never tried that however :)

Again ensure your multigangs dont have any surge protection as this will totally ruin your signal.     if they are  working fine then I wouldnt be worrying, lot to be learned from "if it aint broke, dont fix it"

@Philbert Ok, thank you very much. During these days I observed the stability of my connection through powerlines with the way I described in the last message and with another way: I connected the powerline to the same multisocket in which the router and an electric wire are connected; surprisingly I saw that only yesterday the connection stopped working for four times, and the interruption was longer than one minute only one time. The other days connection stopped working only one or two times, for a maximum period of time that was no loger than one minute. I'm thinking that my powerline adapters are working fine, but during the day they need to do a "timeout" or my electricity provider makes this timeout through maybe a noise in the line or some instability that doesn't make problems to electric devices. Is my hypothesis possibile?