These plugin systems are quite interesting, they allow renters for example to get some benefits of Solar without having to make permanent installs. The systems a lot cheaper than a full setup but obviously don’t produce the same amount of power. I first saw them appearing in France and then since Germany changed the law to allow them its good to see it flourishing there too. This isn’t going to save the planet but its a little step of improvement.
400 Euro isn’t bad for all the fittings and inverter and the big benefit of these DIY systems is you just put them together and connect them to a standard wall socket. Constantly just saves you money on your bills when there is sunshine. Its also not enough power that its worth dealing with export tariffs but in countries where smart meters already exist it could be part of the mix.