getting testimonials

Hi - I'm in need of some advice on how to get testimonials for a product I have just created.

Idea: I am thinking of putting the product out as a free offer at my 'opt-in' box (to my list) on blog. Then, if people on my list enjoy the product or get good results I can email some of them personally, or from FB and ask politely for a testimonial.

The only snag is the product has gone out free to my list for a few months...but the plus is I may be able to get a tonne of good reviews. I am weighing up the benefits to short term loss to long term gain: even if I lose a few sales short term when I go to market with a price tag on it, with so many excellent testimonials from REAL folk who i truly care about, I should gain over the long term as new folk join the list over time...this is an evergreen product.

I did a mini free product once and it was for free at opt in and people fell over backwards when I asked them for a testimonial...so I know it works.

Do you know of any better strategy than above that might work to get real testimonials?? NO I AM NOT into paying people on Fivrr to do it. My niche are full of savvy educated people who can sniff a rat from a mile off...plus putting reputation at stake is a no no for me.

Any ideas or comments on where I could do better?

Thanks!