Finger strength is what sets great climbers apart from merely good climbers. Ultimately it is your fingers that keep you in contact with the rock and therefore they will be the limiting factor in what you can achieve. Neglect them at your peril.
If you are going to buy one item of training equipment then make it a fingerboard. The Phat Boy Fingerboard is a bigger version of our critically acclaimed original Moon Fingerboard but has been aimed at the beginner to intermediate climber.