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.
https://support.wix.com/en/article/transferring-your-wix-dom...
https://support.squarespace.com/hc/en-us/articles/205812338-...
As far as I know, their SEO is fine, though they'll usually do worse in things like page speed than a site built from the ground up. I don't recall any sites my previous employers built with said services struggling to rank in Google.
As for whether they'd be recommended? Well to be honest, I'd say only for small companies and individuals who need the most basic of websites and don't fancy paying very much for it. For a client in that situation, you may as well just throw together a quick site on one of these services, change a few images and colours and call it a day. At least then they won't keep coming to you for web hosting help or updates.
The benefit for clients is that they can pay you once, for a few hours, to help them set it up (if they even need that)... and then they basically don't need you anymore. I've "lost" several happy clients this way, but I'd rather they just use that service than waste their money on a developer they don't really need. It's very easy to use, reliable, and cheap. And they have a single vendor to go for any sort of support they might need for their website.
In contrast to many of the over-engineered Next.js or Gatsby sites I've seen, Wix is far, FAR easier to maintain and I get pretty much zero complaints about it after initial setup. All the other stacks I've ever made for clients, whether they were in Next, React, Angular, vanilla HTML, Wordpress, Drupal, Joomla, other CMSes... all became a maintenance headache after 2-3 years, and usually obsolete, unusable, and completely rewritten within 4-5. Not so with the Wix sites; they just keep going year after year and the client never worries about it again, logging in to post an occasional update every week or so but otherwise letting it do its thing.
I wouldn't choose to use it for a personal project anything more advanced than a personal blog or a very simple marketing site. But it's fine for what it is, and the web is better off for having services like this for regular people to choose from. Not everything needs a super-heavy JS frontend.
There are no real SEO penalties, but as with any web property, you have to do the work to get all the SEO working as you want.
As far as benefits for developers, give me an open source tool any day that I can improve on, extend, or mess up with sketchy coding. These tools are meant for consumers to build their own sites for the most part. They represent the initial commodification of "get a website". They are more difficult and/or expensive to extend than a tool like WordPress, Laravel, Hugo, etc. And they are walled gardens, which means they are difficult to migrate away from.
Wix doesn't let you move your files.
But cost wise, $20 a month is nothing. The first time they run into a WordPress security, theme, or extension issue, they'll spend more than a year's worth of Wix hosting to hire a dev to fix it.
But they still use Wix CDNs like wixstatic.com and parastorage.com. I wonder if those are blocked too...
Wix is overly complicated bloat, and you are better off just using WordPress if you need the bells and whistles or Squarespace if you don't.
Compared to Wordpress, though, either is much simpler because they're fundamentally site builders as opposed to CMSes. With Wordpress you really have to think about concepts like "schema" and try to understand posts vs pages vs comments, and it gets way more complicated once you start adding in page-builder plugins or ACF or SEO optimizers or performance enhancements... Wordpress is way more powerful (and thus complex, buggy, and expensive in dollars and time) than any of the "build your own website" services, Wix or Squarespace.