An effective testimonial
should have the the following elements in them:

1. Specific - Be clear about what the product did for you. Not that
you love the creator and the product owner is a nice person. Generalities mean
nothing.

2. Comparative - What was life before the product compared to life
after the product. That's why those before/after pictures in weight-loss
market are so effective.

3. Illustrative -give a case study if possible.

4. Believable - avoid superlatives (another way of saying "be honest") and just say what the product did for you.

5. Vision casting -what you hope to do with the new benefits you now enjoy.

Hope somebody finds this helpful.