Back when I was brewing one gallon batches (and using "fizz" drops) I ended up with a "3 & 3" approach for bottle conditioning - 3 weeks conditioning, three days in the fridge. Never had a problem with fizz drops this way.
Late last summer, I had a small batch of a holiday beer that I wanted to condition/age for 4-5 months. So I split batch down the middle - every other bottle was a fizz drop, every other bottle got two grams sugar. I didn't see a difference in carbonation between the bottles.
For me, fizz drops worked as if they were sugar - just a little slower.