[TowerTalk] one more TailTwister question

[FireBrick]

See an ad for a used TailTwister control box.
I don't need it, just curious as to what makes a series 2 rare?
Didn't find any mention in rotor histories or on HG site.

CDE TAILTWISTER T2X ROTOR CONTROL BOX SERIES 2 RARE 
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Sex is like air.....it's not important unless you aren't getting any. 
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Bill H. in Chicagoland
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