I spoke with someone at Ghostshield and they recommended the Eco-Etch 1001 (non-acid based) over the Hydro-Etch 1000 (acid based) due to the fact that I was going to use the product indoors. To be precise, I needed to clean and etch foundation walls on a 100+ year old home with heavy efflorescence prior to using Ghostshield's 4500 densifier and their 8510 sealer/waterproofer.
The Eco-Etch 1001 did a great job cleaning and brightening the old concrete and was easy to work with, however it did not completely clean up the efflorescence. Now I will try UGL's DryLok Etch and if that doesn't do the trick I'll use Ghostshield's Hydro-Etch 1000.
If you are working on cleaning up any masonry surface with a significant amount of efflorescence, I suggest you go straight for the Hydro-Etch 1000 and don't waste your time with the Eco-Etch 1001.
This is an excellent product! I used it to clean and etch a concrete basement floor. It was far easier to use than an acid-base cleaner. Specially, considering the closed in area. Although expensive, I would definitely use this product again!