As far as finding it easy to migrate to Pinegrow from Blocs, I’m gonna have to go ahead and say, “no.” Blocs is a drag & drop visual designer. While Pinegrow has some drag & drop features, and some great visual tools, it is considerably more complex software with a higher learning curve. You either need to have at least a basic understanding of HTML and CSS, or a strong desire to learn, to really be able to build a site painlessly in Pinegrow. It’s more of a HTML/CSS editor than a visual builder.
The upside to this is that by learning Pinegrow, you are significantly adding to your website building skills, and your value as a front-end builder. The downside is that it will take a strong desire to learn these skills and not get frustrated because learning to code takes time. Pinegrow can do almost anything, but it doesn’t stop you from doing things that can “break” your layout.
If you are looking for a solution that is more similar to Blocs but that supports Bootstrap 4, you might want to check out Bootstrap Studio, or Mobirise. Both support Bootstrap 3 and 4, are available for the Mac, and are more similar in look/feel to Blocs. They’re also very reasonably priced.
Personally, I have all of them, but I use Pinegrow the most because I build a lot of custom sites for my clients, with a lot of hand-coding. One of the cool things about Pinegrow is that you can build sites in any program, and bring them into Pinegrow to tweak them, or do things the builders can’t do.