If I understand your question right its 10.5 inches. The screws near the emitter are LED module retention screws (there is no switch to wedge it against) so the blade insert is about 3.5 inches. Precise adjustment will vary.
Interestingly, the Brood Guard is just an Initiate V4 without a switch hole attached to the tonfa adapter. The threading for the two sections is MHS compatible so the length you asked for could be adjusted through use of other hilts and adapters or TCSS parts.
I was also considering getting the Brood Guard and was wondering if the brood guards pommel area can be coupled to a saber to make an alternative staff..?