We have one - great for playing music, asking what time it is, getting the weather forecast. Basically, all the stuff you can't do on your phone, laptop, or tablet.
I purchased a smart light bulb for grins and giggles. The set up was more complex than expected, and I had to install an app from the bulb mfg on my phone. After set up and config, Alexa can turn it on/off with voice commands. That is neat, but not actually worthwhile given the cost and complexity. I have already forgotten what I named the damn bulb, so not sure what command I would use to turn it on/off.
To make purchases, you have to install the app (skill) and set it up - so it is not like if you get one of these you are automatically at risk of getting random products in the mail.