The patent bar pass rate is typically less than 40%. But there are all sorts of clowns taking the test who have not adequately prepared and are hoping to get lucky. While that won't happen (you won't pass the patent bar by luck or sheer smarts), if you are smart enough to get a degree in engineering or science, you are smart enough to pass. You just need to study.
In my view, taking the patent bar without a commerical review class is a complete waste of your time because you will not pass. You will need to pony up the dough for one of the prep classes. I'd say the only people who don't need to take the classes are people whose full time jobs relates to patent applications (e.g. patent examiners, people who work at law firms or corporations preparing applications, etc.) But they still need to study.
As you've figured out by now, you don't have to go to law school to take the patent bar. A nonlawyer who has passed the patent bar is called a patent agent. A lawyer who has passed the patent bar is called, you guessed it, a patent attorney. You just have to have an undergraduate degree in engineering or the hard sciences to take the test. You can also qualify to take it if you have sufficient coursework in these areas even if your degree is in something else.
Where do you work? Some companies will gladly pay the review fees for their scientists and engineers to take the patent bar.
If you are interested in writing patent applications, then take the patent bar. It certainly will open doors for you if you are interested in working for a corporation or a law firm as a patent agent. The primary responsiblities of a patent agent are working with inventors to draft patent application and "prosecute" the applications to issuance at the Patent Office. Patent "prosecution" is NOT the same as patent enforcement or litigation, which involves asserting an issued patent against someone else, e.g. filing a lawsuit for patent infringement. Patent agents usually don't do much in that area. Some companies that are heavily involved in patent litigation have patent agents review patents of others and comment on them, but usually attorneys do that.