Try it out. They have a free 2 week trial. And with some digging around, the videos, and the forum, you will be able to figure out more than you think.
As a designer myself, I chose Squarespace because I found that my own design sensibilities would get in the way of my ability to build my site. I would get hung up on the design of my site, when all I really needed was something simple and elegant that worked nicely and allowed my work to be the star. That being said, Squarespace was affordable, easy to use, and comes with beautiful templates that are highly customizable. The templates are easy to use, and for the most part responsive, which is a huge plus. I would say one of the only problems I have with Squarespace is the help section, and section where you can look and ask others questions and get answers. It is sometimes confusing or hard to know if you are getting answers on the right template or not, as different templates require different code injection.
For my personal site its pretty basic. I just use photos and text, with a link to download my resume and visit my highlighted social media. I also have a contact form that potential clients can use to easily contact me. I also use Squarespace when designing and doing websites for clients. I have built a wedding website for a friend on Squarespace in which I used the feature that linked up the guestbook to a Google Drive spreadsheet that kept track of people's well wishes for the couple. I also used it to create a website for a local artist. That site utilized the MailChimp feature so she could keep in touch with buyers, but also had a contact form and shop. Squarespace has performed perfectly for me. As a designer, it has easily opened up the ability for me to offer simple website solutions to clients that I normally would not be able to do. The best part is handing certain controls over to a client while holding back some so they can't fully break their own site. Clients can edit and add content, but not touch any major design elements.
Well, I have listed pros in my previous answer, so I will summarize here. Pros are: ease of use, client-only portal control, price, and design.
Like I said I wish the help section was more clearly divided by template, so you can go to your template and find the answers that directly relate to the type of site you are working on.