holy crap is right...man what an awesome piece of equipment. Does the "Besieged: 100 MP" replace the 20 mp? Either way, it's a fine piece of equipment. Wow...
It's hard to find a decent ACC+ pair of pants for mages (sometimes for most jobs), although these seem like a winner!
And if I am corrent, the stats mean that normally, outside of Besieged, you receive ACC+6 and MP+20, but during Besieged you receive ACC+6 and MP+100 (which now makes these pants much more useful than just for skill up or random melee give or take for not having any other useful stats to them).
Unless the price of Vendor's Slops goes down (well, at least on Valefor server), these bad boys may be a decent choice for certain jobs.