Working very well. We use both the hidden BU field in the form and overwriting the BU value in our Automated workflows just to make sure our new Contacts are assigned to the right BU.
The only issue we have found to date is some Contacts are overwriting the values of existing Contact records - we believe this is when they submit forms using other people’s devices or computers (due to cookies). The solution here is to go to the HubSpot form that is automatically created for your Gravity Form, edit the form and go to Options, and switch on the option to “Always create contact for new email address”.
Important note - Each time you update the HubSpot intergration inside Gravity Forms, it republishes the HubSpot form and by default turns this option off, so you need to go back and turn it back on whenever you make any changes in your Gravity Form!