I've got similar issue like you before so I would say pick or keep your Piranha cause it can withstand major water parameter for awhile while you're away from home, while with ATF thing easy when wrong even with 5~10 mins power out, or your kids running around and tap on your glass tank and spooked it = you have a dead ATF

My 17" GAFT ended up dead just like that when a kid sudden tapped the glass (all kid pretty has same behave with any fish tank LOL) and the GATF just dash like a rocket to the tank wall then go up hit the locked top cover...floating around for few mins and its gone! What can I do to the kid? They were laughing cause it look really fun to them without knowing they just killed the fish....