@Alciel: They're not for-profit, though, maybe that's where the misunderstanding happens. It's to help pay for buying the magazines and manga needed to do their work as well as keep their site running to keep distributing their chapters. (https://www.patreon.com/jaiminisbox).
As the page states, these are generally young college-age kids spending out of pocket to provide this kind of quality. Anyone who remembers those days knows money is hard to get. They put in all that work and just want appreciation for all that work they put into it. That being said, you are not at all required to donate (the also get ad revenue, it's just not enough), they just appreciate it since it helps them out. The chapters are available on JB early, not just to advertise their site, but it helps them indirectly. They just ask other distribution sites for a cool-down period, in a manner of speaking.
On the flip side, these other sites use an algorithm to steal from sites, not just JB, watermark it, and literally pass it off as their own. By supporting sites like those, sure you'd get the pages sooner (frankly you can get the pages just as soon from their site), but you are supporting the sites that steal it and effectively giving them money since the sites also earn ad revenue, though more-so than JB. Meaning, you are funding their stealing.
So to directly answer your question: The difference is you can support the guys who actually do all the hard work or support the thieves, never mind the fact you can get the desired chapter for the desired manga at the same time.