Experience From - Dr. Bill Misner, Ph.D. ,
Having worked for physical therapy clinics and 2 division I universities (with athletes) these past 13 years, I have seen both of the braces relieve patello-femoral syndrome(PFS) in some athletes, but not all.
A brace is a brace any way you cut it, and it is the goal to get the muscles that surround the knee joint to balance the forces that apply to the position of the kneecap (Patella) and the compression impact of the femur as it moves on the tibial surfaces.
The braces you speak of compress the patella tendon against the bony surfaces of the tibia and femur making less force compression on the posterior surface of the patella, which is covered with a very sensitive cartiligenous covering. When the patella glides too far laterally(in 90% of PFS), the catiligenous surface becomes "scratched", swells, but because it has a poor blood supply, it heals very slowly and hurts like &*%$.
The braces take some of the pressure off, which is why your 20 miler was less painful. If I had you in a clinical setting, I would be working on biofeedback and electrical muscle stimulation devices to help you teach the quad muscle (Vastus MedialisOblique-VMO) on the inside of your thigh to tighten and contract earlier so that this muscle will "guide" the patella in a less lateral direction during the running gait.
In the meantime, if your do not have a therapist working on this with you, straight leg raises with ankle weights done with a quad tightening before raising the leg have been observed to help correct the "lazy VMO". Doing leg extensions(last 30 degrees of extension), with a bolster under the back of your knee with weights on your ankle also may help to correct PFS....If that is what caused your need to get braces. Again, the goal is to run pain-free and brace-free as there is no substitute for natural muscle balance.
I recommend that you get this instruction in a single session from a reputable Physical Therapist who sees runners on a regular basis. Here is hoping this helps, because I know how you feel, I suffered for 2 years with this problem and wore my Cho-Pat daily before orthotic correction and strengthening the muscles I mentioned above corrected the problem. And now at age 57, I run a minimum of 15 to a maximum of 40 miles per day 6 days per week...It is not pretty or very fast, but it is good for me and better than running in pain.