checkboxes instead of multiple

First of all: Thank you for your module. You have saved me a lot of time.

Now to my suggestion: Unexperienced webusers have sometimes issues with multiple-selects. This problem can be solved by using the type "checkboxes" instead of "multiple".

Additionally it might help to add Javascript that deactivates the checkbox "All" on the selection of another element and deactivates all other elements on the selection of "All".