Looking into the American Standard Heritage® 2/4WCX3 Heat Pump packaged system. Is a unit like this one really all that inefficient compared to an older 10 SEER split (placed in a very hot Florida attic)?

Only after I mentioned it, 2 of 3 contractors told me that I can save $ with install and R-8 duct replacement (mine are metal, but too small in diameter and leak) by installing 2 packaged units. This would replace my current 10 SEER RUUD split unit with the air handler in the attic.

The main issue is that my ducts are too small and leak (and need replacement). I cannot find a contractor excited about replacing ducts with the current split system since accessing them is very difficult on one side of the house. My attic space is less than 4 feet at the top (with very limited access).

With 2 packaged units, the 4 supply runs from each would be @ 18', 15', 10', and 8'. The 2 return runs from each would be @ 20' and 12'.

Call me a control freak, but I like the idea of having 2 complete units (servicing especially) at each side of the house, each with their own Tstat... Could I have the filters at the 2 returns, and not inside each packaged unit, itself? If the Tstats are set the same, does anyone forsee any problems (units working against each other...)?

I know that split systems are ideal (and the most efficient), but my house is not ideal. Also, I am in need of blown in insulation, but I want to get the duct issue resolved before I have that done... Sorry for all the questions. I need someone to reverse my leaning toward the 2 packaged units if needed. Many thanks!