Bi-Slob would make a terrible trainer. The controls are too fast, and the flying characteristics are completely unique. The construction is also fairly light so they're not terribly crash resistant.
They're pretty worthless for Balloon Bust for the same reasons. The control response is vague, the lack of precision and sudden, wild changes go against what you want when you're trying to hit a balloon. Two up isn't too bad, but the finesse required to keep the lines tight and the aforementioned control issues would make Bi-Slob combat a good way to destroy a Bi-Slob but it'd be anything but relaxing.
Build a Bi-Slob. Build two. They're extremely simple to scratch build, the stabilizer/elevator are cut from a single sheet of 3/16, the fuselage is a simple box with an engine crutch/firewall/gear mount, and a couple square formers. The hardest part is sticking to the plans for the control system ratios, engine offset, tip weight, etc. Even if things aren't exactly right, it'd be hard to tell since they fly fairly random anyway. They're lots of fun, but completely in their own class of model.
Old pics...


