So, I suppose the method is to learn the 20 5-letter words and the key that goes with it?
The thing is the words don't mean a thing and are not necessarily easy to pronounce. It doesn't really feel like less work than learning the digits straight.
Remembering words is different than remembering digits; mainly because remembering digits is actually remembering words that represent them ("five", for example). Therefore remembering digits would actually require you to remember 100 words instead of the current 20 which you then "decompress" into digits in your head using the simple decoding key.
The thing is the words don't mean a thing and are not necessarily easy to pronounce. It doesn't really feel like less work than learning the digits straight.