I've had no need to try the CSS injection capabilities, but I did need a substitute for Tampermonkey as of Safari 13, since App Extensions are now required. This fits the bill perfectly! It does have the downside that I need multiple copies (or symlinks) for a script to run it on multiple domains vs. just the script header doing that, but on the upside I can keep my scripts in iCloud and have them run on all my Macs without worrying about keeping them in sync! It's also much faster than Tampermonkey, but I think that's just because App Extensions run significantly faster than old-style extensions.

Seems to work perfectly for injecting JavaScript into sites by domain. Just create JavaScript files named <domain>.js. It doesn't handle matching specific paths on a domain, but you can of course implement such functionality in the script itself by reading the page location. I haven't tried the CSS functionalty as I already use other tools for that, but it should work the same way.

Thank you for the OSS contribution, made me that much more willing to actually buy this. Does exactly what it says and (if you have coding knowledge) has a very straightforward workflow.

Ens***tified user-antagonistic policies plus lame react tricks to avoid adblockers are nothing when I can use vanilla js to find all promoted posts and remove them.