Very well done! Now to clear up some things about the bike. One, yes it actually rides and is stiff. The only place where is flexes is right where it is suppose to at the dogbone. The plastic hinge area on the top tube. They climb very fast and also work better then a typical mountain bike in deep sand. There is a bit of learning to be really quick in a technical single track trail. This is because the bike is alive and the geometry is changing a bit. After a while you know what the bike will do.
This frame is a second generation. This frame had a tendency to fold in under a heavy braking load. We also owned a third generation slingshot and to address this they made the seat post a larger size and dropped the top tube to connect lower down onto the seat post of the frame. That bike is the yellow one in my profile picture. Very well done with the bike I will say indeed.