That Flea thing is really nasty. First-off he says keep your thumb perpendicular to the neck. So when he has index down on F and middle on F# you can see his thumb is indeed perpendicular. Then by the time he has ring and pinky down on G and Ab his middle is out of position and the index is pointing backwards for no good reason. He teaches that one should keep the thumb perpendicular to the neck. But watch how his wrist, and with it the thumb/hand joint, is moving up and down. Are we to believe that every time his wrist moves his thumb is following along, remaining perpendicular? Of course not! Unfortunately the lighting is terrible and there are no shots of the back of the neck, but here ...
View attachment 5066163
... you can the contact point of the thumb is not moving. By the time he gets to the Ab with pinky his thumb is poking out behind index and is about 40° to the neck, i.e. 50° from perpendicular:
View attachment 5066172
This thumb pivot is a crucial aspect of all methods but he totally fails to mention that he is doing it all the time. But the flying fingers are also really not a good example to set. Fine if you are a 'character' player but not the stuff of good teaching. Don't just take my word for it - check out 2:21 - 2:26 in the Jim Stinnett video!! If I had to recommend one over the other it would be the Jim Stinnett every time.
That said, in the lower positions, as you already noticed, Jim is not always consistently close to the fret with 1FPF, and you can hear quite a lot of extraneous noises.
My personal preference is a Simandl-like approach with a 1-2-4 or 1-3-4 in the lower positions, which gets the fingertips much better placed for clean stops and, important to me as a fretless player, pitch-perfect intonation. I then might switch to 1FPF above 5-7, depending on demand, key etc. And almost certainly 1FPF above the octave. In lower positions it is easy to use 'extended' fingering (to play intervals such a m3) in lower positions using thumb pivots without over-stretching the hand. Using the pivot the thumb stays in position but the whole hand moves up a half-step or even a whole-step. You then pivot back or the thumb follows on to faciiate a 2-step shift - hand then thumb. Ascending, the thumb leads the shift, again in 2 steps 1: extend the thumb back to locate the new position 2) the hand follows on and falls into position around the thumb. So although I might be playing say F with index and Ab with pinky, I don't really consider this a 1FPF because the index comes away from the F and goes over F#, yet the thumb doesn't move - it pivots.
EDIT - I will add one more point, which is that I see a lot of talk in technique discussions about economy of motion and staying in position. TBH, I think bass players would do well to put extra work into accurate and secure shifting. It is very much the bogeyman when it comes to technical elements - get confidence with shifting and you will soon start to not really care if you are playing 1-2-3-4, 1-2-4, 1-3-4 or anything else. Start by playing scales up and down on 1 string...
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I know we are talking about left-hand here, but it is all in the detail. Check out 5:00 - 5:21. He is recommending strict alternation, but twice in a row he fluffs it. First time he plays
1-1-2-1-2-1-2-1-2-
1-1-2-
1-1-2, then in the second attempt he goes
1-2-
1-1-2-1-2-1-2-
1-1-2-
1-1-2
He consistently plays the first two notes of the scale 1-1 (except when he tries not to) and consistently rakes with 1 on the way down. In the second example, where he starts 1-2, see how he drops in a 1-1 in the next pair to 'reset' and defer to muscle-memory. Not saying it is right or wrong (and who am I to critique Jim Stinnett?) but he sure ain't doing what he says he is.