It's not quite so good! I think we need more people to try it out.
In Linux, you can configure it. You can choose between Windowed and fullscreen (the code for that doesn't exist in FJ-GL for Windows yet), scale from 0.5-32x, set filtering to linear rather than nearest, and even decrease the number of sides that are approximated to make up circles and ellipses to get a little more performance (at great cost to visual quality, mind you). That last one is important for my Gravity demo, drawing a circle of radius 400 would go down to 1 FPS on Sphere_GL, but it stays up near 100 FPS on FJ-GL. Of course, that's also because FJ-GL actually approximates a circle and uses polygonal rendering rather than going pixel by pixel deciding if it's part of the circle or not.