Just like any other audio equipment you can spend as much or as little as you want for a sub. I have a decent pair of floor speakers that I added a nice Velodyne sub to. It makes a difference and works well with movies too. I use the WiiM Amp with that setup and the app is pretty straight forward.
On the other hand, I have a home full of Echo devices to listen to music. I've added an Echo Sub to that mix and the Echo Sub (or any sub) makes a huge difference in rounding out the sound from the tiny Echo speakers.
Point is, you can get a decent sound out of a less than audiophile quality sub, but if you want tight refined bass you might need to invest a few more bucks.