Question about rail king watch man shanty

From the RK Shanty instructions it appears there are 2 controlled circuits, albeit 1 at a time.  An isolated rail only operates 1 circuit.  

Many guys use a relay triggered by the isolated rail to convert its 1 circuit to 2 circuits.  There are many OGR threads describing DIY circuits for this fairly simple relay circuit...maybe $5-10 in parts but does require messing with components.  There are also off-the-shelf relay modules for $10-20.

The ITAD also drives 2 circuits but is triggered by the optical beam looking for a reflection from something on the track.  The additional feature of the ITAD is you can set a time-delay which can improve visual appeal of the effect - see the description in the Shanty instructions to decide if this is something you want.

The ITAD aims an invisible light beam at the track and looks for a reflection.  You can adjust the sensitivity to detect a reflection from the more distant parallel track.  Many guys find that increasing the sensitivity makes the ITAD trigger on ambient light and hence become somewhat finicky.  It's truly one of those your-mileage-may-vary situations with workarounds like fabricating an awning or something to shield stray light from hitting the ITAD light sensors.

Like you say, the less expensive Realtrax ITAD is like a lock-on plugging right into the track section while the Scaletrax ITAD has screw-terminals for the wire connections so you can locate it with a bit more flexibility.

Here's an insulated rail relay that has an isolated relay that can be configured for this use if you don't like the ITAD.  You can wire either track common or center rail to the relay common for various switching configurations.