First a word of warning. While normally the fact that an app is in the Mac App Store would mean that it has been heavily vetted by Apple, and therefore we would recommend it as safe, there has been a case of an app - specifically one used for cleaning your Mac - being found to be stealing data from machines.
The app, macoptimizerpro, was found to be collecting data from Macs and sending it to a specific address. Apple has since removed it from the store. We recommend that anyone using Dr Cleaner should stop doing so now.