The ballistics of the .25 ACP are WORSE than the .22LR - 'Nuff said.
Obviously, any gun is better than NO gun, as long as it shoots reliably, but I would seriously look for something with more power than the .25 ACP.
I personally would want nothing smaller than 9mm or .38 Special.
Regardless of the caliber, good shot placment will trump twenty misses any day. As that young motel clerk in SC recently found out when she killed the man that was trying to rape her, who outweighed her by more than 100 lbs and towered a foot over her, with a single point blank shot to the chest with a .22LR caliber pistol.
Of the .25 Auto, firearms legend Jeff Cooper once quipped,"... carry a 25 if it makes you feel good, but do not ever load it. If you load it you may shoot it. If you shoot it you may hit somebody, and if you hit somebody - and he finds out about it - he may be very angry with you."