As a non-pro, I needed one drill that handle all that I could throw at it. I purchased the CSX in advance of building an outdoor bbq table using Philippine mahogany. I used kreg pocket screws for the frame construction (2.5" and 1.5" pockets / screws) and I found that the CSX would struggle to drill the holes and even have a hard time driving some of the screws. I was also draining the battery every 20 mins or so. I really wanted the CSX to work because it really is a thing of beauty.
The dealbreaker ended up being that the chuck would not hold my 3/8" and larger bits. I could deal with the relative weakness of the drill for boring out holes in hardwood (using the slow speed was necessary in most cases), but not being able to use a bunch of my bits was too much. Half way through the project, I returned the CSX and purchased the C15 with the right angle and eccentric attachments.
The C15 just flies through the mahogany but it is much larger / heavier than the CSX. My next Festool purchases will include the router and domino before considering the CSX again.
My $0.02 anyway.