So..... says it works with flooded lead acid batteries and AGMs, not gels.
Maybe that means there are some unsealed AGMs out there in the battery world, although I've not seen any advertised. All AGMs I've read about are valve-regulated, sealed. The Optima is a sealed battery, IIRC, and were it me, I wouldn't try to pry it open to add anything, including distilled water
Maybe the product has the same effect as equalizing batteries... but even doing that depends on the manufacturer's recommendation... and most makers don't recommend equalizing their AGMs.