While on the subject of hydrogels....
Terra-Sorb is a hydrogel made by Plant Health Care (PCH). I always stress that this stuff is not a magic-bullet watering substitute, but can help in the event the homeowner misses a scheduled watering..... forgets, long weekend or maybe a short vacation etc etc. I think using a hydrogel also makes the warranty issue a little easier- not only did you select a vigorous, healthy plant, you installed it correctly AND even used a hydrogel... if it dries out and dies after all that, it is fair to say the blame falls squarely on the shoulders of the client. In short, there is nothing more you could have done other than water them yourself. I also find that hydrogel/mycorrhizal supplements are a good selling points and add relatively little to the overall cost of the project.
I'll add that one nurseryman I know warns that hydrogels can cause problems for plants that prefer drier soil (some perennials, grasses), particularly if the gel is concentrated around the root ball. I can imagine a scenario where an employee simply dumps this stuff in the hole and covers it up, creating a layer or pocket of pure hydrogel around the roots. When properly applied I don't think there would be a problem.
Hydrogel is incorporated in
PCH Tree-Saver, which also includes mycorrhizal fungi. Seems to help in those situations where you know the trees/shrubs will get no love other than what mother nature provides.