I'm a network engineer so I have a "proper" setup at home: fiber-to-the-home, enterprise-class network devices (access points, switches, etc.), and so on. We were at Best Buy a while back and, while browsing around, I saw some of these "powerline" adapters on the shelf and, mostly out of curiosity, decided to buy a pair [0] of them to see how well they worked; I was doubtful of the "1200 Mbps" claim on the box.
For testing, I plugged them into AC outlets along the same wall in the same room, with ~14 feet separating them. After getting them linked up (very simple), I connected laptops to each unit, manually assigned IP addresses to the laptops, and used iPerf [1] to run throughput tests.
I'll spare you my rant about them but peak speeds were extremely disappointing, just shy of 50 Mbps. I honestly didn't expect anywhere near the advertised 1200 Mbps but I was expecting speeds relatively close to what I can get over my existing wireless. 50 Mbps may be quite acceptable to some, especially if one's Internet connection isn't that fast, but it was far from acceptable for me. They would also randomly "freeze" or "pause" for 20-30 seconds at a time but I didn't really investigate that issue.
[0]: https://www.netgear.com/home/products/networking/powerline/P...
[1]: https://iperf.fr