25 guys with a machine set on free play means it will certainly need repairs. Does your son know how to repair a machine? Will he have the money to hire someone? Will some of the 25 guys be irritated when they want to watch TV or study but a loud pinball machine is making that impossible?
To me it seems the better idea would be a foosball table because its cheaper, nothing to really break besides one of the soccer figures who can be cheaply and quickly replaced, is quieter, and easier to move. Plus when some kid spills a whole pitcher of beer on it it can be easily hosed down.