The good:
- Smooth and easy builder
- Detailed design options but without overcomplicating
- Ability to create AMP pages
- Resposive customer support

The "need-tweaks"
- You cannot currently change the canonical tag (in order to point to your original page on another website). This means that I can't use this to create AMP versions of existing pages (important for SEO). Support told me that this is coming in an update, but I don't see it on the roadmap yet. I'll stack more codes if this happens soon because this is my most valuable use case.
- Sometimes weird things happen in the interface (ex. click a 3-dot menu for shadows and the options appear on the other end of the screen). These bugs are very few though.
- AMP pages are not as fast as I expected. LCP (Largest Contentful Paint) is over 5s, and overall mobile speed rating around 70 (pagespeed insights). This is fast compared to most websites, but I get similar speed with highly optimized Simvoly pages (lazy load scripts etc.).
- No global blocks / header / footer.
- No audio player module (although you can add amp-audio code in an html code box as I did in the page below.

Here's an AMP page I created using Swipe Pages:
https://amp.string.systems/d2-guitar-chord

And here's the original page which I replicated:
https://string.systems/d2-guitar-chord

Overall this has huge potential. I'm waiting to observe the response of the team a bit more before I decide to upgrade to 5 codes :-)