You have to ask yourself, "why is it free?". The answer is simple, when you are connected to a VPN the computer (server) you are connected to has full access to your connected device. This allows your data to be interrogated in the server, and files can be injected into your device.
If you think you are safe when you stop using a free VPN, think again, if viruses have been injected into your device, every keystroke can be logged, even when you are not connected.
you can not guarantee speed, and who want to keep switching every time you want to watch something that is geo blocked.