Checkboxes should be used to change settings, not to make things happen. If I understand correctly, you're proposing using the box itself to change the state and using the label as a click-tip. I see the following problems with your proposal:
- In contrast with a ? icon, it is not clear at all that clicking the label will display the tip.
- You are effectively reducing the click zone, which means that your users will take more time to change the box's state.
- If they don't know what each criterion means, they will have to click on all labels till they find what they want. However, this is also a problem with ? icons, in which case a tool-tip (where you just hover over the icon) could be better.
My suggestion is to change the wording of each criterion, so that it is clear what exactly will be filtered when the user clicks on the checkbox without the user having to dig for descriptions.