If you're doing absolutely no optimization on your sites and using a bad host (shame on you) then RabbitLoader may help you. Otherwise, you're going to get significantly worse speeds out of their CDN, image optimization, etc.

It has been about 24 hours on a very small site (so it's all cache'd etc.) and my site speeds have significantly declined.

I did some tests with the original setup which is a host CDN (Google Cloud CDN) paired with Shortpixel for image optimization, and WP Rocket for cache and other optimizations. My scores were 100/98 but that's never the important part, the load time varied between .55 to .83 seconds. I turned off WPRocket and used Litespeed for a bit with a score of ~97/92 and load times varying from .97 to 1.18 seconds.

Then comes RabbitLoader... My score went back up to 100/98 but who cares about score when the load time is slower? The load times have varied from 1.46 to 2.42 seconds and in Lighthouse for mobile, 2.3+ seconds.

So, while this optimization tool may give you better scores, it's very deceptive because the overall real-world speed is significantly slower. I'll continue to test in the coming days on a few sites and update my review but as of right now, it will be a big return.

Buy it, though, just don't think it's something amazing. Do your own testing and make your own conclusion. My conclusion is that good hosting with a good CDN plus my own optimizations are infinitely better than RabbitLoader will ever achieve.