I've fooled around with it a little bit, so let me give you the report.
First, as for Catastrophie, like I have mentioned before the damage is little on the 'meh' side. The first screenshot is me using the Catastrophie with a WAR sub. Since there was a little inbalance in the actual damage I present to you a screenshot of Catastrophie actually doing one of the better damages. When used, it drains HP of about half~1/4th of the damage done (there is a resist factor in play), so it's perhaps very useful for soloing purposes? It also goes through Blink/Utusemi, so it might be useful in Ballista too. There is no difference in damage at TP100% and TP300%. With Sneak Attack Catastrophie damage hangs around the 1400 mark.
Now for the Apocalypse. First of all the "Additional Effect: Blind" on the weapon activates at a high rate. Versus a Very Tough Decorative Weapon it activates once every 4~5 hits. As for how useful that can be, well, I can't really tell. w Also, there seems to be a hidden effect of "sometimes DMG value up" in the weapon, as I sometimes hit the enemy with damage that even goes above the maximum possible damage according to the DMG number. It activates at a rate of about 10%, similar to the rate of Double Attack activating. At the current moment I'm trying to figure out if this is a random effect or if there is any specific conditions to keep it activated constantly. That is all.