1. Get 8 party members

2. Attune three of these to each party member

3. Cast Charm Person once every hour, using a different pair of glasses

4. Profit

Or four level 20 artificers. Then they can use their infusions to get four of them and craft the rest.

Or four level twenty wizards who made charm person their signature spell, effectively making it a cantrip.

Is it locked to only casting at 1st level with these?  Or can a warlock with all 5th level slots cast it at 5th level?

Since the spell originates from the glasses, I would guess that it's locked at 1st Lvl. I think it functions like a spell-storing item, except that the glasses cast the spell whereas the spell-storing item simply "produces the effect," meaning that the glasses could be counterspelled... and even as I type that, I realize that the glasses wouldn't necessarily be "counterspell-able."

To your point, I would expect it locked, but I could see a DM being convinced otherwise. That said, I'm quite new to DnD altogether so I don't have much exp. with standard practices in the hobby.

Honestly not a fan, def not worth an infusion slot for sure. 

If it allowed you to inflicted the 'charmed' condition with a save, it'd be amazing, but basically just storing a spell that lets the victim know they were charmed ain't exactly that helpful.