I was very happy with Buenaley and their NIE service. They were very quick and provided personal support via WhatsApp. I got my NIE in exactly one week, which is quicker than the 10 day estimate they provide.
The website and the process to provide my details worked great and it really took me only 10 minutes, without any of the frustrations that is so common in digital processes. After filling out my details and confirming my identity (which took 2 minutes) I got a few updates via email but didn't have to do anything and could forget about the NIE until it arrived a week later.
Highly recommended.