Rick,
I have talked to the guy that makes the Harlan unit a few times - good guy and he knows his stuff.
I was looking for something a little more unique and I couldn't find it, so I built it instead. The shift light I made consists of an anodized aluminum housing with either a stainless braided or plain black cable. 3 wire hookup (switched power, ground, tach signal), and it's really small compared to most lights (about 1.75" long and 3/4" across).
Really the differences I put in are it works with 1 to 15 cylinder engines without any pills (yeah I know, nobody has a 15 cylinder or a 7 cylinder, etc). It can operate 2 lights, so you can set up "shift soon" and "Shift now" lights. It can be set that the light comes on below certain RPM's for example if you want to avoid bogging the engine, you could have one of the lights come on if you're RPM's are below 2000, say. I also set it up to work in 50RPM increments instead of 100 so I could get a little finer control.
Basically, a shift light will work or it won't. A Harlan, Autometer, or any other light will work and do what it's supposed to. What sets them apart is the price, features, and looks. I was more interested in features and looks for my light than the Harlan or Autometer units offered, and the Autometer I wanted was $199, so like I said I started making 'em myself