I’m not too sure about the extender. You could probably just raise the tailgate to the higher attach points for longer items (like the plywood capability). But perhaps that wouldn’t be high enough?I think the extender could be useful. With it out, makes the bed about on par with my Sierra with the tailgate up - and I can put my kayak out over that just fine. With the tailgate up on the SC, there's no way I could do it. The angle would be too steep and I'd have a good 7 feet hanging off the back. The extender would give a better angle for long items to overhang. 8 foot 2x4s, for example, would be just fine laying over the top of the bed extender, but probably wouldn't be a safe load with the tailgate up and the same boards laying over it.
Ultimately, a lot of that will come down to individual uses. Some people will find it useful, others will definitely not see any need. It is a shame they couldn't find a mounting style that would allow it to be clear of the brunk opening though.