It is important always to use definitely the latest firmware, the latest updates have brought significant improvements. Otherwise, there are certainly many things you can do wrong when you install and which then leads to unsatisfactory results. So try often announced.
Just as an example: The dehumidifier was too close to the devolo adapter - disturbed> transmission. Our TV stands (currently unfortunately no alternative) a bit tight on the adapter. During the operation then the transmission rate drops schonmal extremely off, so it because (fortunately rare) can provide "reception problems" - to explain: we use entertain TV via Telekom VDSL.
Otherwise, I have some pictures for your information our system, shown in devolo dLAN Cockpit, stationed with the customer images.
My conclusion: The whole thing is a great networking solution ..... but where it can be done I would still clearly prefer a LAN cable, even if the time should be somewhat more complicated. Since everyone has to incorporate his personal expenses / pain threshold :-)