Andrija, backlinking is not only a form of appreciation, but the way the internet works. In terms of SEO, this also good practice, since you are basically duplicating content from another site and search engines may penalize your testimonials page for doing so.
By adding backlinks (or a "source" link) where you took the content from, may even help you in ranking better. Why?
- Target site has relevant information to your page/s
- Target site may even backlink to your product page (just make sure you both are not baclinking to each others same page; So your page A links to external page B, that external page B links to your page C [not back to your page A])
- Gives your testimonials/in the media page authority
I wouldn't worry so much about it. Just make a nice page, backlink to their pages where appropriate and carry on ;)
Place backlinks to the source information and you're all good.