Andy Ricewrote a review of Gregory 3D Hydro Reservoir on August 13, 2017
Familiarity: I've put it through the wringer
This is an awesome reservoir. Easy to fill and keep clean, and no weird plasticky taste. The bite valve took a minute to get the hang of, but have no issues on the trail with it. The 3L size fits in most packs in the daypack size range, and larger. I would think a smaller day/hiking pack would be a tougher fit for the 3L reservoir just because the size of the pack. To be safe, I would recommend the 3L for packs about 18-20L and up.