@jjvw I too scratched my head when I read that bit about "frequency tuned" coils. Have no idea what that means. ..
As I recal, 'Frequency Tuned" was something that dates back to when Jim Frens designed the original Nth degree springs for the TJ/LJ. i don't remember the details, but it has to do with the frequency response between the front of the Jeep and the rear of the Jeep. The idea is to dial in the spring/shock combo between the front and the rear of the vehicle so when you hit a dip or big bump the front and the rear of the vehicle settle back into normal ride height at the same time. This takes into consideration the vehicles wheelbase as well as weight distribution. Some people might not notice the difference. Others, like me, will be driven nuts by a vehicle where the rear end doesn't settle in as quickly as the front or vise versa.
I have a good friend who used to have a JKUR with the AEV system and recently traded it in for a JLUR. I always thought that JK was the best handling Jeep I had ever driven or ridden in. Its an over used expression, but I really thought it was better than stock. My friend says he likes his JL better. He says the linear rate springs feel more, ahhh linear. He thought in some cornering situations the AEV springs felt too soft and it was noticeable when they hit the firmer rate. However, he never mentioned that issue until his AEV shocks had nearly 100,000 miles on them. So its not really fair to compare AEV shocks with 100,000 vs brand new JL setup.
Anyway, for me, I am a huge fan of AEV. If I ever get a JK I will put an AEV suspension under it. I don't even need to think about it. Nothing else comes close as far as I have experienced. (Which is admittedly limited.) However, the JLUR is a little diffent. Because it can run 35's on stock suspension, I'm not sure I would want a 2.5" lift. I would be very tempted to just throw on some 1" pucks to gain a little better breakover and call it good.
Now, the whole argument about a soft spring and stiff shock vs a stiff spring with soft shock is an interesting discussion to have. A soft spring with stiffer shock might give more options for tuning the ride via shock absorbers because the springs aren't the limiting factor for a soft ride. However, if your going to carry a load those soft springs will suck and you will be wishing you had a stiffer spring with a softer shock. Thats only the compression side of the equation. The rebound, which I think is arguably more important in how a vehicle feels will also be greatly affected by the spring/shock combo. I don't have the knowledge to really give an analysis of the differences, but I could sure speculate how they might behave. It would have been very interesting to listen to the Jeep engineers or even AEV engineers (who I believe consult with Jim Frens, a former Jeep engineer) weighing the pros and cons of these options.