PlayerEmers - thanks for asking. The performance of Box2D+ is about the same as the standard Physics asm.js plugin - mine is, essentially, just a later and more complete version of Box2d. If you're aiming for mobile then my recommendation is you should only market to top of the range hardware. Make some tests using the standard plugin and see if the performance is good enough on the hardware you're aiming for. If you need prismatic joints, gear joints, gravity attractors, proper collision filtering and a physics based platform behavior in addition to the standard plugin's revolute joints then Box2D+ is probably what you're looking for. If you're not sure then don't buy this plugin just on the off-chance - it really has more to offer than the standard plugin, but performance increase isn't one of those numerous benefits because it's about the same.
thank you for replying
yeah i will see how things go when the project goes foward, testing peformance in some devices, etc... if everything is ok until peformance/gameplay tests end, i will just keep using the default physics behavior
but in a near feature, i'll probably buy it for other types of projects
its looks too damn good to skip it