I know this is an old thread, but I wanted to add my experience with using the FrontRunner folding UHF Antenna mount.
I bought the antenna mount when I put the FR tub rack on the back of the ute. I had my UHF aerial mounted on the roll bar behind the cab and I liked the spot. Happy to accept that it didn't work as well back there - it was better than having it wobbling around in my field of view on the bullbar or nudge bar, and when I've had aerials on Z-brackets out of the bonnet they always rubbed the paint through and squished the cable. Behind the cab it was protected from most branches and animal strikes, and still worked more than well enough for my purposes.
The mount itself is well-made, and there's really thoughtful design elements like the angled guard underneath to protect the cable entry. The powdercoating is fantastic, and it looks a treat. One of those things that you're really happy to receive and unpack.
When I first fitted up the FR mount, I had a thin stainless Uniden whip aerial. Around town it was OK, and I'd often keep the aerial at the 45-degree position so I can get into my garage / undercover car parks / etc. When I was out on the open road though, and with the aerial positioned vertically, problems started to come in. At 100kph the wind would push the aerial over into it's 45-degree position. On a recent gulf trip with a lot of corrugations, the antenna would fall all the way down and end up pointing to the ground. As you can imagine, it did wonders for my radio reception (and scratched the paint on the body of the tub - no real loss there). Tightening up the tension screw didn't seem to help - even with it quite tight (such that I *almost* wasn't able to rotate it by hand) it would still rattle down. Tightening it up also seemed to make a bit of the problem worse - it would push the outer part of the mount (that the aerial mounts to) away from the body of the mount (that attaches to the car) and put a sideways pressure on the centre pin/bolt such that the two wouldn't sit evenly/parallel against each other.
I've now replaced the aerial with a heavy-duty, metre-long GME fibreglass antenna. The heavier antenna, of course, makes the problem even worse. Even driving around town now makes the antenna fall down - not what you want for an expensive new aerial! I've adjusted the tension screw up even further, but no good - the mount is basically impossible to rotate by hand now, but at the same time it doesn't seem to want to lock into any of the positional detents either. Just driving around town is enough to make the aerial fall down. This is a problem because the car doesn't fit into the garage with the longer aerial on it now, so I can't just fix it in the upright position!
I feel the problem is with the little spring-loaded locking pin/bearing. It just doesn't locate into the positioning holes strongly enough. I'm not sure if I got a bum one, and it doesn't locate properly? I guess it's by design - if the aerial hits a branch you want it to fold over to protect the aerial. However, unfortunately for me, there doesn't seem to be any way to stop it folding itself back from just general wind pressure and bumps and rattles of normal driving. I think they need to redesign it with some sort of positive locking mechanism - a pin that you can remove, tilt the mount, and then re-insert to lock it in that spot (or similar). It'd be no good for avoiding tree strikes then of course, but it would actually let you set the antenna at a position and have it stay there.
I'm not entirely sure what to do about it now, to be honest. I think I'll probably end up pinning it or welding it in the locked upright position. Of course, then I'll have to get a shorter aerial to mount on the spring base for around town, and only fit up the brand new big aerial when we do a trip away. A bit disappointing really, as it's quite an expensive part to start with.
Keen to hear if anyone else has had a similar problem and if you were able to fix it.
Cheers,
Matt