The BV-20 was Unertl's version of a shorter scope for field applications or target work. Although no longer made, that model is still popular with Unertl fans.
I personally am not a big fan of external adjustment scopes, but to each his own.
That scope on eBay is priced right at value, maybe up to $500.
The autonomic nervous system provides for involuntary muscle function - the work of breathing, digestion, and so forth. On some folks, that's a pure waste of ingenuity.