I always get whatever potassium and magnesium glycinate (more bio-available than oxide, and available in 100mg pills, so I can spread it throughout the day) are available in the biggest bottles for the best price- not that Amazon is significantly better than all the other evils we've been discussing, but I subscribed to this potassium when it was $7/bottle and this magnesium when it was $11/bottle. The prices fluctuate, but running out of either was a terrifying prospect during lockdown. If I can find them more affordably anywhere, I just skip that month, but I'm spoiled by the convenience.