The sound did not consistently work but, worse, when it did it turns off when the screen goes to sleep! That really does make it impossible to use.
This is a pretty typical problem with non-native applications. You save a bit on the development but you really do pay with quality. They just never have the feel of a real native application. The really big issue with the iPhone app is if you have a major problem, it's at least a 10-day turnaround to fix it with Apple's app store system.