I have a Toshiba smart TV. It's painfully slow (several minutes to turn on the smart functions), to launch Netflix or Youtube. Most of the "Smart" applications are obsolete, or outdated - the company stopped updating the firmware after the first year. So now my TV is 4-years old and the screen is perfect but the software is bad.
For $35 ChromeCast added all the modern functionality to my TV. The operation is flawless, all the apps supporting ChromeCast are happily casting to it and we're having lots of fun with my kids when everyone has control with their phone.
The installation took 10 seconds: plug the HDMI into the TV, plug the USB cable into the power outlet... done. The software part was even easier. Installed the app, it found the ChromeCast device immediately and even sent to it the wi-fi password, so I didn't have to set it up.
Bottom line: a high-class device, perfect solution for non-smart TVs.