Almost any type of splint or cast is going to be uncomfortable and somewhat inconvenient. The idea of immobilization is usually to give the arm a rest so the injured soft tissues can heal. Taking load and stress off the area helps prevent microtrauma that could delay recovery.
Preventing motion of the forearm, wrist, and hand certainly does restrict activity. And some devices are more restrictive than others. For example, a recent study showed when comparing casts to splints a definite difference in the amount of forearm motion that is allowed.
A long arm cast that includes the wrist and elbow is able to prevent forearm rotations (turning the palm up and down) better than any other method. Other immobilizers such as a short arm cast or removable splints reduced the amount of forearm rotation by about 60 per cent but did not eliminate these motions.
The short arm splint allowed the most amount of forearm rotation (more than half the normal range-of-motion). Splints also come in different ways — some are prefabricated and one-size-fits-all, whereas others are custom-made to mold to the individual perfectly.
There may be a better type of prefabricated (off-the-shelf) splint that would work better for you than the one you have. Or it’s possible you will just need to put up with the discomfort and inconvenience long enough to foster healing. It’s possible the nurse practitioner who saw you and knows the condition of your arm/hand may have some practical suggestions. A phone call to the clinic may help you sort out what your options are.