Moving iron and induced magnet designs are usually considered subsets of the moving magnet category as they typically have similar output and are attached to the moving magnet input on your preamp or receiver. The difference is that magnets are fixed in place and a piece of iron moves in the magnetic field to produce the signal rather than moving a tiny magnet.
Only you can decide what the JD9 buys you. Do you like the flexibility of using either moving coil or moving magnet cartridges? Does the JD9 offer a performance enhancement over the C30 that you don't want to give up? Yes, you might have to adjust the JD9 to work best with whatever cartridge you use with it. It's also possible that the C30's phono stage will simply sound better to you.
Only you can decide what the JD9 buys you. Do you like the flexibility of using either moving coil or moving magnet cartridges? Does the JD9 offer a performance enhancement over the C30 that you don't want to give up? Yes, you might have to adjust the JD9 to work best with whatever cartridge you use with it. It's also possible that the C30's phono stage will simply sound better to you.