A 3 day class such as you describe can be useful in that it may serve to stimulate your thinking.
Know this, however: The usual "seminar guru" formula is essentially the same as it was 30+ years ago: draw them in to a class that is more conceptual/introductory in nature as opposed to true, genuinely substantive "nuts and bolts", and then upsell them.
IMO, the only time it makes sense to enroll in a backend course or "mentorship" program is IF the course/instruction is COMPLETE and the help that you'll need is readily accessible-- meaning that you're able to get the answers to questions that pop up as you go along and get deeper and deeper into things.
You can do extensive reading about note investing, or any subject for that matter, but it's only conceptual until you actually get out and do it. A fair # of people on these BP forums are seemingly able to take that first step, or get a good start after reading/interacting through this site.
Having said that, if you're like me, concepts don't really "sink in" or get internalized until you have an actual potential "deal" or transaction to check out or pursue and you've got to execute the steps and do things that you don't yet know how to.
In my experience, many people have trouble or get tripped up at certain points along the continuum. That's where it may pay to have someone with experience to consult with-- one question/step at a time, generally speaking. That's how I got my start in this business 22+ years ago. I find that credible mentors like I had are really hard to find these days, so I consider myself fortunate.
The big key is finding the right person, course, mentor, etc. who will give you a GOOD "bang for buck" along with SUBSTANTIVE direction that you can use WHEN you need it. (And, if we're talking about $ THOUSANDS of "bucks", run-- don't walk-- away from this person.)