If you're recording on an iPhone 4 or iPhone 4S (or earlier) you may experience some slowness or lag when using the app. In most cases this is because the iPhone 4/4S is not designed with enough RAM to fully utilize all iOS 7 features. This doesn't mean you will be unable to use the app on an iPhone 4 or 4S. However our app is optimized for iOS 7, so it does mean the app may perform slower, and less reliably until you record using a newer iPhone (with more RAM) capable of handling both our app and the processing power requirements of iOS7.
I've found that following our Battery Troubleshooting Instructions tends to free up much-needed memory for the app, and helps it respond quicker. As always, please submit a support request if your slowness is beyond what you'd expect and our team will investigate.