My truck runs antennaclimber's GP controller. It works great! Highly recommended. (As far as I know, it's also the only viable option if you need a new GP controller.)
If you're running a 30-year-old GP controller, it might be wise to get a spare. I'm no electronics expert, but my original GP controller had charred parts and burn marks on the board. I'm pretty sure that's a bad thing... It also didn't work.
I'm also a fan of the GP override, in case something goes wrong with the GP controller. But I want a working controller in my truck, if only so others can drive it without needing to understand the intricacies of manual GP management. For me, I run antennaclimber's GP controller, and I keep one in my spares kit. I also plan to install tim292stro's manual GP override kit, once it's available. I *really* don't want this truck to get stuck deep in the mountains.