Like Guido, I like Lincoln but have also had good luck with tractor branded guns, e.g., NH and JD.
Of course, the tractor manufacturers do not make the grease guns that they sell with their names on them but major brands usually try to assure that the accessories that they sell do not tarnish their reputation.
If your husband has large greasing projects, he might want to consider a battery powered gun. If he already has a battery powered drill and/or other tools, perhaps he can find one that uses the same battery that his other tools take.
Anything but an early adopter, I bought my first battery powered tools about a month ago. A battery posered grease gun is next on my list.