They can be very difficult instruments. Now a six headed microscope is not all that hard to maintain. If teaching is part of what you do you need to look at a dual or multi-view module. They make teaching far easier and directly interactive. Since all manufacturers include a pointer system on their systems you can easily point to the important features of the specimen.
Most manufacturers have a lighted pointer controlled by a joy stick on the multi-view module.
While this is a great convenience it is also a problem. The problem is that most manufacturers use a separate power supply for the pointer bulb. Its real easy to forget to turn of the pointer and burn out the bulb. Some third party makers are using fiber optic cables to get light from the microscope bulb and bring it to the pointer. What this means to you Multi-view heads can make teaching a lot easier.