Does using my phone connected to Invizbox increase my protection when using my online banking ?

Maybe.

Online banking utilises HTTPS to encrypt your data to and from their website. HTTPS traffic is secure, however not private. Whilst a VPN will provide additional privacy, some online banking websites will prevent access when you try to connect whilst using a VPN.

That said, you should not use public WiFi to access your online banking as it could contain unknown threats which could compromise your security. In these cases, utilising an InvizBox Go will increase your security by encrypting your traffic between your InvizBox Go and the online banking website.