Mules are test devices (microphones, BMWs, Ducatis) that have been intentionally disguised so as not to reveal the final released design any earlier than needed.
A couple of people said they liked the mules. I refer to these designs as "South Beach". The three mules here have been used for ribbon motor development and for field testing. This is different from so-called "beta" testing. "Beta" usually means the product is actually released, but it allows the manufacturer to pull the product and change it in case it sucks.
On one hand, the customer becomes the guinea pig, but on the other, the customer gets to have first crack at something new.
If you are an early adopter, get the beta, but if you're a pioneer, get a mule!