I have a 503, a Rocketeer without the built in patterns, and have cleaned up a few Japanese ZZ machines. The ZZ machines are much heavier and therefore give the illusion of being more solid. I found that they were much noisier when operating and vibrated more, but were faster than my Rocketeer. My ZZs had external, more powerful (I think) belt drive motors, the Rocketeer has an internal motor which can be much harder to fix or replace if it gives you problems. If I have a bigger sewing project though I use the Rocketeer, but have not used it for more than straight stitching or zig zagging.
The real solution though is to make room for 2 machines!
