Stack is 13", seems like the doubler is about 6 or 7" longer. (Just checked ORD and it says "The overall length of the Doubler™ is now 21.5" for all versions", so that is 8.5" diff)
To me, the weight is the biggest win vs a 3:1/2:1 doubler. Shorter would actually hurt mine, but then, I have a 115" WB.
I would forget LoMax. They've been promissing that for *years*. And with the Stack, Atlas-4, and WMS 3:1, they've let their market slip away. Why finish now what they didn't finish when they would have owned the market?