That's an insane cost reduction -- $250/month is a common gray market price in the US.

How do you ensure the safety and consistency of anything?

Asking for a friend.

Use stairwaytogray, find a supplier with a history of many many 99+% purity reports from 3rd party testing sent to janoshik, then order 20 vials from that supplier, then either send a vial to janoshik yourself or participate in a group buy test (or just wait for someone else to test the same batch. At that point, it is very likely your ampoules have the same purity and amount. The best supplier seems to currently be sigma audley.

That's the darknet level of drug addicts safety. For poor & desperate much better than nothing, but certainly not without its own risks