Anyone running a (Brownie) trans?

[Greasey Harley]

Yesterday the shifter busted off out of the NP435 in my '68 C10.
clean brake right down at the pivot pin.
It was stuck in neutral and the Little Blue Truck got to ride home on a roll bed.
While I was shopping around for a replacement shifter today, I came across a 68 3/4 ton with a 435 4 speed, and a 3 speed Brown-Lipe (Brownie) aux transmission.
If you're not familiar with them, they are an UD/DD/OD gear box that sets behind the stock trans connected with a short drive shaft.
They require a secondary shifter located behind the stock shifter --->Twin-Stick

I don't know that I want twin sticks in my little truck, but I DO WANT OVERDRIVE.
anybody have any experience with one of these?
I am going to buy it, I can get the entire set up including drive shaft for cheap. Sounds just weird enough to be cool and it fits my budget
Just wondering if anyone has any experience with them. thoughts or opinions.
How do they shift, how tough are they, worth the effort, etc?

-Russ