To break our options down...
Auditory Seviroscope
+Simpler to make
+Could be of great practical non-research use
+Portable
+Constant stream of information
+Might be better for easing Eike and Egrimm into Windherding stuff
-Not very detailed, would require effort to draw useful information out of it
-Probably needs another wizard with auditory windsight to write something on how to interpret results for research
Visual Seviroscope
+++Highly detailed, easily-understood
+We have two LMs with visual windsight to work with
+Would be of direct use to studying Bok and similar one-off weird stuff the dwarves run into
-Harder to make, and expensive
-Bulky, non-portable
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As for the Rider... I really think we should take the potential tactical upsides of each as the main deciding factor, rather than the potential aesthetic upsides and downsides. Regardless of how it looks/what animals we're attached to, miscasts will always happen.
- Horse-mounted variants: Would be great at charging infantry in particular.
- Are centaurs bascially included in this, as far as potential weaponizing goes?
- Giant boar: Probably similar to horses, might be some slight differences in terms of how strong or how fast it is
- Demigryph or giant cat variants: Will use all limbs to kill, so extra good at making a single enemy's day really bad
- Winter Wolves: Good at pursuit
- Spiders: Can probably climb walls and maybe enemies
Anything else aesthetically - looking like wraiths or like Mathilde - carries its own set of advantages and disadvantages which I think we've already discussed extensively.