I can't answer your question directly because I'm not familiar with the Mahasi method. But I'll say a word on similes.
Similes are excellent at encouraging comprehension of a concept. They literally illustrate it and as they say, a picture tells a thousand words. How much more so does a story of pictures as a good simile provides?
However, similes have their limits. As they are stories, their relevance to reality is always restricted. In the end, reality has to be faced directly without any middleman.
Good luck in your practice.