I'm running the Flex-a-lite setup in my truck. Now that I got the temp probe mounted in the upper radiator hose, I like them a lot better.
I got my fans used off a friend of mine. They were 5 or 6 years old when I got them. I had to replace one fan blade that was stripped out, the VSC, and I recently set up the temp probe in the upper radiator hose. Temps stay about the same as they were with the old mechanical fan. I've only pulled 12k with them and they worked just fine. I don't really watch coolant temp, but oil temp on that trip got up to 218* for a little bit cruising at 75mph and once i slowed down to 65mph temps settled in between 210-212*. I pulled some hills on that trip, but no crazy hills that went on and on for miles on end. Just normal Texas hill country rolling hills.. Up hill, then down hill, then back up hill all the time.
I changed the VSC and fan blade when I first got them. I've run them for a year and a half and only changed the temp probe because I suspected they were turning off while cruising down the road with the air moving over the temp probe in the radiator fins. So far I'm very happy with them.
Worth $600? Probably not to most people. I guess it depends on why you're doing them. I did them just to prove once and for all whether they work or not rather than just hearing people say they won't work when they haven't tried them. I went through the trouble to convert my OBS to an SD radiator just to be able to run these fans and I don't regret it one bit. I won't be going back to a mechanical setup for how I use this truck. If I towed 20k, I probably wouldn't try them. I didn't really notice any power difference like some people want to think they'll gain by switching to e-fans, but that doesn't hurt my feelings. It does seem a tiny bit more responsive off idle, but nothing to get excited about. It runs just like it always did when the fan clutch wasn't engaged. My truck did drag down a lot when the fan clutch did engage though, so I don't have to put up with that. It's just like driving any other truck, but there's no fan clutch to engage and drag the engine down a bit. Hope that makes sense and hope it helps your decision.