Custom website or Squarespace?
A site builder is the correct choice for most small businesses. The question is whether you are in the minority it holds back.
Is a website builder good enough for a small business?
For a brochure site with a few pages, a contact form and a menu or service list, usually yes. Builders are fast, cheap and maintained by somebody else.
Anybody who dismisses builders outright is selling builds. Most small businesses do not need anything more.
What pushes a business off a builder?
Speed on mobile, integrations the platform does not support, and structured data that the template controls rather than you. Those three account for most of it.
Performance is the most common. Builder templates carry weight you cannot remove, and on a phone on patchy signal that becomes people leaving before the page loads.
Can I move off a builder later?
Usually, but check the export path before you commit. Some platforms let you take content and structure with you and some effectively do not, and finding out at the point of leaving is the expensive way.