If you are seeing keyboard lag (i.e. ranging from a bit slow to non-responsive) on your iPad after downloading a new version of iOS you are not alone. We've had plenty of reports of this and it's not an Inzant specific issue, its an operating system issue that weirdly doesn't affect all devices, or even all apps on the same device.
Most of the recommendations gradually work up to doing a reset on the device (basically setting it back to factory defaults). This is a pretty major step as it'll involve reconfiguing everything from scratch, not just re-downloading Inzant Sales Plus again, so we'd generally recommend getting in touch with Apple Support prior to this just in case they have a quick fix for the issue.