Ask HN: Are Squarespace and Wix sites worth it?

I’ve been involved in web dev in different forms for 20 years, but I’ve never done anything with these types of websites.

My questions are:

* When you register a domain with them, is the domain legally yours?

* Are there any SEO penalties for using these apps to build websites? Does anyone own a website or client site hosted on Squarespace or similar that’s ranking high on Google?

I can see the benefit for developers but I’m wondering about the benefits for clients.