IME intonation is all about holding good consistent posture in the hand and accurate shifting of the hand as a unit. Fingers should not really be wiggling around within the positioned hand as this ruins overall posture. My daughter's 'cello teacher agrees, and with his beginners has come up with something along the lines of what you suggest... It is his exeperience that for beginners starting off this way, use of such a device in higher positions is not necessary since good posture is already adopted from learning first position.
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I should add that this is not just a line of tape, which only gives position reference. It is actually a raised ring with a depression in the centre that locates the thumb vertically for position and laterally, on the crown of the neck, to assure the correct attiitude of the fingers over the fingerboard, with no collapsed or locked joints.
Just one caveat - we have no direct experience since my daughter was already an advanced player before working with this teacher.