Installing VPN on my three Apple devices which are two iPhones and one iPad

Nope. If you are doing this thinking you are making your devices more secure, then that will not be the case. Any site you visit or data you enter on that site is being sent to the VPN company. Many of them will sell this information as that is their business model.

There is a use for VPN's and that is to securely "tunnel" into work computers for remote access. This is how they were intended to be used and later started being marketed for security and being able to avoid region restrictions from some services. When you see marketing in those cases, you cannot be sure that they are not just looking to monetize your data.