Cloudflare currently forces us to sign up for a Pro plan just for the “Signed Exchanges SXG” feature. In my opinion, it should be free of charge instead, or could be offered for a lump sum or something. Let’s see why.
First of all, this non-standard feature is supported by Chromium/Chrome and some of its derivatives, but not by other browsers.
Also, Chrome claims to support it, but there’s no guarantee that the whole mechanism will work or speed up the page. The reality is, ultimately, only Google Search decides if it’s going to work, and not Chrome. See also some complaints that appeared in this forum.
On the whole, AMP pages, which I don’t like because they’re not standard either, are a better choice. As a matter of fact, they are much lighter than the original HTML pages, and don’t have much JavaScript. Therefore, they are much more likely to be loaded quickly, regardless of Google Search. Sure, Google can show them in the SERP’s, thus “promoting” them, but that’s another story, because we can use/read AMP pages anyway by typing their URL. On the other hand, this is not true for SXG. What’s more, even if Google Search decides to deliver a “signed” page, there’s no guarantee that it will be loaded faster, for example in the case of AMP pages themselves where the improvement is negligible.
That being said, if you also need a Pro plan for other reasons (more page rules etc.) it definitely makes sense to subscribe. But if you just want to try out SXG, it doesn’t.