HubSpot recently showed me this message:
Nothing wrong with it per se, however this message is more misleading than you may think. From the message alone it seems like I will only benefit by upgrading. "More module fields", "better template previews", "more modern coding experience". All seem to be like improvements,. So I clicked upgrade. And oh boy - when I tried to edit one of my many templates suddenly I could not add HTML fields or HubL fields any longer - the backbone of the template I have been using.
So after you upgrade, there is this small link in a corner of the screen explaining in more depth that Upgrade Tools is equal to "Transitioning from V1 to V2 modules" which comes with drastic changes, including the deprecation of HTML/HubL fields. The solution? Easy - just rewrite your templates using modules. So a 5 minute job to make one small change to the site now involves me needing to rewrite the entire template. Without any heads up warning from HubSpot.
There is a tiny icon on the screen where you can revert back to the old tools, which is cool, but hard to find. The whole process is retarded.
If you want your users to upgrade to the new designer, please be transparent and also warn your users that the upgrade has backward compatibility breaking changes and that upgrading might require rewriting of templates. Be transparent. Don't be a politician or a lawyer or a doctor or realtor or sales person.