Even I would prefer them in our walls it’s quite some work so went for the easy option as well.
Exactly, why spend more?
My folks live in a bungalow so we got some external cable and routed it behind the guttering/facia so no need to trash walls. Worked fine.
Mine have always been plugged into an extension and I’ve never had issues. It needs to be as my BT socket is at the bottom of the stairs next to a single socket. Don’t know if it makes any difference that it’s one of these ones?
Works fine for most people & for sheer ease of use & convenience, they're definitely worth a go (easy returns with Amazon if they don't work as expected). Also, they should always be plugged directly into mains sockets only, so not to be used in multi-plugs or cable extensions of any kind - here's where the pass-through ones come in handy. Perhaps you only tried them with multi-plugs? If yes, there's the main cause of your problems.