I made an update to the extension to fix the error you were getting so that the MRT server behavior can be updated.
There were still some issues with the updating of the repeated regions and hidden form elements and form element names associated with conversion that are more difficult to solve.
Updating MRT from mysql to mysqli might just require more steps for now. Here is what I did:
1) update the repeat regions to the latest (just open and apply after updating the recordsets to mysqli)
2) remove the old mrt hidden form elements, and form element names so that they are in the state they were in before applying the original server behavior
3) Then open and update the MRT server behavior and let it re-update the form element names and add any necessary hidden form elements.
I've done that for you on the product_update2.php page and uploaded it. Please download it and take a look and let me know if you have any questions.