1.) Why would one want the 40L over the SP?
2.) Does the Troy BUIS come with 2 actual apetures or is it a single with and insert like the ARMS?
3.) Why should I shell out the extra cash for a troy (which I like) over an ARMS 40L SP

Quoted: 1.) Why would one want the 40L over the SP?

Smaller profile (helps if your scope has a large lens), also it's apertures are on the same plane

2.) Does the Troy BUIS come with 2 actual apetures or is it a single with and insert like the ARMS?

2 Apertures

3.) Why should I shell out the extra cash for a troy (which I like) over an ARMS 40L SP

The Troy is built stronger IMHO.  It locks in the up position (the ARMS is held in place by springs - each method has it's advantages & disadvantages).

I had the opportunity to handle both the Troy rear BUIS and the ARMS #40L at a recent show.  The Troy seemed more solidly build and locked in the up position.

The Troy does have two actual apertures on a pivot.  They "lock" into place but modest finger pressure is enough to flip them.

The default aperature is the "large" aperature, which I prefer.

After handling them both, I went with the Troy rear BUIS even though its price was higher.  Thanks, Pennsylvania Defense Consultants!

I just bought the Troy too!