It is generally easier to collect a urine sample from a dog than a cat.
But once cat owners get past their initial resistance in their mind, they usually can find a method that works pretty easily for them. Cats that use the outdoors to do their business will be the most difficult of course.
ThePetCheckup manual describes several methods (for both dogs and cats).
The one I like the best and have found to be very easy is to put a plastic garbage bag on top of the litter pan. Just lay it on top. Since cats like fresh litter, do it just after you have changed the pan or added some fresh litter. They may step on the plastic and be surprised, but they will go ahead and pee.
Just take your sample with the dropper, remove and throw away the plastic bag and you are done! Because you are only testing every 3-4 weeks, your cats will soon forget that anything abnormal happened. And you only need less than a teaspoon of urine (10 drops actually).
Cats are more flexible than we often give them credit for: if I am in the room when one of my cats is heading to the litter pan, I sometimes get a look from them that seems to be saying “are you going to test me now or should I just head over?”