How do you rate it now, almost a year later? I've been playing for 50 years, but a functional mastery of slap has so far eluded me. The TalkingBass lesson seemed the most focused and comprehensive of the many I've checked out.
I too was "slap challenged". Palm-muting on flats was my go-to, so when I recently switched to finger-style, I had to learn all about muting. Fortunately, I did not succumb to a fret-wrap.
My 5-string isn't the best for slap, so I picked-up a 4-string. Round-wounds and low-action is key. I don't care about new strings. I even slap on my 5-string with flats now, but that B-string does get in the way. I am fussy about EQ, but like variety, so my EQ varies with the song/vibe.
With the above as context, I would say "
If even I can do it in my early 60s, you can do it!" I am still slow, but have a pretty clean sound and fairly even beat for what I do. What I lack is stamina, because I just play for myself.
Personally, I like Mark Smith's material on TalkingBass. Like me, he is a "techie" (but dedicated musician), so he breaks things down in sort-of an engineering style. Easy little chunks that add-up. I bought both slap volumes. If I had nothing else, this would be my pick.
I also want to mention Phil Mann on Scott's Bass. He's an ex-boxer (but also a dedicated musician). Both his standard notation and slap courses are great, though in the style there, he can get a bit chatty.
Slap is quite varied. I would not say new, since the double-bass guys were doing it before electric bass was invented. Unlike conventional finger-style though, which itself has variations, there are lots of different ways to slap. It is worth trying a bunch of YouTube videos to get a feel.
I do feel both "slap" and "double-thumb" are needed. Some guys go with one or the other. "Pluck" works with both. Slap rings-out more, and places your finger in a better position for the pluck. Double-thumb gives you more speed, and more fundamental.
To get over the initial hurdle, just sit down 15-60 minutes a day and do the basic beginner slap drills. First week, maybe just get a nice thumb-slap. Next week, start plucking the octaves. Just don't wait too long to try double-thumb. Slap is all in the rotation of the wrist. Double-thumb keeps the wrist straight and uses the thumb like a pick. At first you will feel like "this is nuts", but when you come back the next day, you find the drills quickly start to stick.
There are MUCH, MUCH, MUCH better players here. Many recently helped me figure-out what Marcus Miller was doing on the high-notes (turned-out to be pluck/slap). I just want to say if I, who struggled with it for years due to lack of good instructional material and mental blocks can do it, you can do it.
Finally, a huge help for me was slowing-down videos to see what folks like Marcus Miller are doing. YouTube allows you to set playback speed, but messes-up the audio-quality. I prefer Transcribe!
Transcribe! - software to help transcribe recorded music An hour or so of watching Marcus Miller at 50% playback speed helped so much!