1. Can I play back the video at any tempo I choose?

YouTube has a built-in setting that lets you change the play-back speed at 0.25 intervals. You can achieve a much finer interval if you are using i-phone, iPad, a MacBook or PC.
For iOS, we recommend the app called Vidimote available on the Apple Store for $2.99. It is an extension for the Safari browser which allows you to change the speed of video playback in steps of 0.05.
For PC users, we recommend the following free apps.  Please google "video speed controller" or click on the following links.
Chrome video speed manager.
Firefox video speed controller.
Click on the "available on chrome" tab and proceed to install. After installation, when you open a YouTube video, you will find a box at the top left corner that lets you speed up or slow down the video. The default interval is 0.1. To reduce the interval further, click on the red icon with the double arrow that appears on the top right of your browser and go to setting. There you can change the step size to anything you choose, such as 0.02 and click save. You can also control the speed by pressing the key S to slow down or D to increase the speed.
We have not been able to find something that works on an android phone. Let us know if you know a way!

2. Why do you have two sites selling the same pieces? How are they related?

We do have another site https://smartsoloist.com that sells similar piece. What is being sold there is a software that works only on Windows/PC computers. It has many functions and allows the user to adjust the tempo down to each individual note. The current site is designed for Apple users, or customers who prefer to play the video on a mobile device. These two products are distinct and need to be purchased separately on the two different sites. If you have already purchase the software and would like to gain access to the mp3 file and the videos of the same piece, or vice versa, we offer a 50% discount on your additional purchase. Please write info@smartsoloist.com.