As for the value of such training, in my experience (and I delivered many auditing courses, both accredited lead auditor and non accredited internal auditor versions) is the caliber and experience of the instructor. When I instructed such courses I would do my utmost effort to bring real life cases, relatable scenarios, so people would feel engaged.
If the instructor knows the material and even the body of knowledge well, but is not able to relate the issues at hand with day to day working situations, the course can be the longest and most boring course in the ISOsphere.
Sidney is totally correct, you might end up with a slide flipper with nothing to fall back on and a "deer in the headlight" look if asked any real world questions or to elaborate. You might also get someone who has a great deal of background but lacks the ability to convey their body of knowledge into something coherent, understandable and useful. Both types abound in the training world in a more abundancy than the fleas, ticks or chiggers in my Arkansas back yard, and another slider flipper to boot.....I refer to type instructors as "Shake & Bake Experts".
Me? I've over 200 Lead Auditor courses under my belt a ton of internal ones along with a bunch of other ISO related training courses I wrote, modified and/or delivered. I delivered my last course in 2016 when it was evident that flipping slides, talking in a monotone and having the personality of a dust mite was good enough to deliver material......But that's me and my private opinion.
Unless you're a tad on that masochistic side, have unlimited time on your hands and/or someone says "Ya gotta" don't do a Lead, more often than not the average Internal course is even overkill, but go with one...........Again, that's just me and my opinion.