I have been using Alexa for years. I've been controlling my TV and I have WiFi smart plugs. It is super useful and it has never had issues understanding what I was saying.
I have noticed people who have issues they place the device next to a sound source such as a TV or fan or something and obviously this will mess it up.
I also don't understand why so much hate for Alexa. Everyone in this thread just seems like a Debbie downer, shi*ing on everything all the time.