Jess is right to some extent, the closed system does work out just fine if it is maintained properly. However a cracked head gasket is not always what makes the bottles fail. My main problem with it is, you have to get underneath the Jeep to crack that damn CTS to burp the system. 5-90s method of drilling another bleeder hole in the thermostat does wonders for the self bleeding aspect of the closed system as well. Like I mentioned earlier, I've converted 3 XJs to the open system. I did this for 4 main reasons...
A. I like the cleaner hose routing, only needing two sections of heater hose.
B. The way I do it there's no heater valve to crack.
C. I had a ton of trouble with those "football" bottles, and no I didn't have a cracked head or bad headgasket. I bought the "reinforced" bottles with the "better" cap and they still didn't work for more than about a year.
D. I like the true self bleeding aspect of the open system.
And what I've started doing now is not running an overflow at all. I was looking at my Dad's '48 Packard one day and I realized in the older cars they just had a hose zip tied to the side of the radiator that ran the hose straight onto the ground. I know this is not environmentally friendly but I figure if the coolant gets to where it's going to expand that much anyway, it's going to "overflow" out of the bottle. My point with that being, it's one less thing to have in the engine bay. Just my take on the subject.
-Collin