What are the pros and cons of a packaged gas/electric unit compared to a split system (gas furnace, coils, and outside a/c condenser)?

I'm thinking that I could put this gas/electric packaged unit (like a Trane XL13c or Trane XL14c -- not sure which one fits my needs better) in the attic.

My house:
1. Single story 1430 sqft in Los Angeles, built in 1952
2. Foundation = raised with 30" crawl space
3. Insulation= R-30 Insulation in attic; no insulation on walls or floor
4. 13 double-pane windows throughout house; 3 single pane windows in front (16 windows total)
5. Dark brown cement tile roof
6. Exterior doors = 2 (old wood front door with top half of door with glass panes; and new aluminum back door with quarter window)

Where is your ductwork system located?

That is a shallow crawl space?

Generally the downside on package units is efficiencies both AC and gas furnace. However, for your location a package unit might be indicated. The unit would have to be placed outside on a pad (concrete preferred) with good access to your ductwork system. However, if you have existing split system, there would need to be a very good reason to switch to a package system because obviously Bldg modification would be required.

IMO

Installation of the packaged unit in the attic is not an option as far as I can tell and I wanted the packaged unit located where the current furnace is at. There's already electric and gas outlets up there and a return line for water.

Initially, I was not thinking about the building code modifications. I was just thinking in terms of the components in terms of reliability, efficiency, cost, and maintenance. I thought it would be similar to installing a separate washer and gas dryer compared to installing a single unit that does both wash and dry.