Are replacement parts for SteriShoe sanitizers interchangeable (Example: can you use parts from a SteriShoe+ in a SteriShoe Essential?)

No. All SteriShoe sanitizer parts are specific to the model they were designed for. The ONLY exception is the lamps for the SteriShoe Essential. If you have an Original SteriShoe sanitizer, it will take the same lamps as the SteriShoe Essential.