I was getting it confused with the B&C and LaVoce's that also get used in Devs.
That said, tuning it low greatly changes it's output efficiency where it is strongest.
It is, by all accounts, an absolute beast of a driver... but like the other pro drivers, it has its drawbacks for HT and HiFi Home reproduction. It's all about compromise and what the designer is going for.
The Pro Drivers are best applied for their mid-bass efficiency rather than anything lower. I have seen designs where this has been pushed to a 16Hz tune, but it requires a huge box and the output is far from even. If tuned to 22Hz in a Dev with a stepped horn, it is a very different monster, and will have a pretty impressive output across it's band.