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I'll probably start with the scales I can make the longest runs with in 2nd and 3rd Rabbath. I mean, I figure the majority of us were born with 4 fingers and an opposable thumb on each hand so why not make the most of all that?
It makes me wonder if Simandl was just shifty or if his 3rd finger didn't function.
Methods are evolving, Simandl is being legitimately challenged and yes some of the early stage exercises can be quite dull, but it has served the classical string bass players well for over 100 years, and continues to do so. As for the disfunctional third finger - if you decide to work through the entire Simandl method you will find the 3rd finger re-introduced into the method in higher positions. The Bille method primarily uses 3rd in place of 2nd.
The 34" electric bass scale is a good 8" shorter that your average string bass and has very few of the same physical challenges so effectively addressed by Simandl and others. Simandl/Bille are predicated on development of a stable hand-shape that promotes good tone and intonation in co-ordination with the bow. On the fretted electric bass, intonation and tone are largely de-coupled from the left hand, and there is no bow. But stable hand shape and assured secure shifting are just as important to the electric bass as they are to the string bass.
The concepts of pivots and crabs works very well with the electric bass - the shorter scale and the physical position of the instrument with respect to the body make it very natural and comfortable. The shorter scale also makes using all 4 fingers a practical proposition compared to the traditional DB methods. As I said earlier, stable hand shape and assured secure shifting are still important components of a good general technique. In the lowest positions, even on electric bass, the 4-finger handshape is comparatively unstable - try playing the first half of an F minor scale (F, G, Ab, Bb) with fingers 1, 3, 4, 1 without rolling your thumb, twisting your wrist or swinging your elbow.
So, with that said, I would recommend
initially working on hand-shape stability in single positions until you develop strength and consistency using Simandl (1,2,4) or Bille (1,3,4) fingering, or a mix of both. But stick to the position. I would also suggest learning scales with traditional shifts (you will still need this skill) before adding pivots and crabs. And here is why - without good hand condition (i.e. physical fitness) there is a risk of long-term injury if you start with the full Rabbath gymnastics right off the bat. You need to understand what good hand-shape feels like in order to know when your pivots and crabs are pushing the envelope too far.
YMMV