I feel the JP-3 worked awesome on my RTR. Power was more controllable and run time was more than I expected for a .26. Averaging around 8.5 to 9 minutes.
If the Airtronics servo you plan to buy will be the steering servo that arm will be good. You will have to trim the splash guard slightly cause the arm will barely contact it. Or you could grind off the extra hole on the servo arm cause you will only use the 3rd hole out from center to keep the steering geometry correct. I use the blue one just like the one in the link. But the losi arms weren't out yet when I needed one.
Oh I forgot. The upper servo saver piece will wear some over time and create some centering problems. So the aluminum upper servo saver piece is great when that time comes.