A testimonial and a review are not the same thing. A review is left spontaneously by the client at the end of the project and read by Hello Archi: you have no say in it. A testimonial is something you ask for, and you decide whether to publish it.
Sending a request
From the Testimonials page you create a request for a client. A unique link is sent to them; they write their testimonial on a dedicated page, with no account needed.
Reading, publishing, taking down
The submitted testimonial comes to you. You publish it, or you decline it. A published testimonial can be unpublished later. You can feature it on your profile, and attach it to the portfolio entry it relates to.
What stays out of your hands
You choose what you publish, not what the client writes: a testimonial cannot be edited. And the same rule as for the portfolio applies: if it contains a way to reach you or to identify the client, do not publish it.
It works exactly the same way for a company.