is disk drill a safe ap

If you are trying to recover data from a physically failing drive, then most standard utilities (even data recovery apps) won't work since those apps and even macOS itself are unable to handle the errors produced by a failing drive. The more you use a failing drive the more likely the failure will get worse where even a professional data recovery service will be unable to recover any data.

If you are just trying to recover accidentally deleted data after emptying the Trash, then this app should be safe. If you are using an SSD though the data is most likely gone for good especially if the SSD had TRIM enabled. However, you the data you are trying to recover is from your main boot drive, then you need to stop using the Mac immediately so you don't accidentally overwrite the data you are seeking. You need to boot from another drive in order to run the data recovery software. If you have access to another Mac, then you can put the Mac with the Use target disk mode to move files to another computer - Apple Supportdata you want to retrieve into Target Disk Mode.

chelseaFC4 wrote:

is disk drill a safe app

Probably. What do you want it for? It may or may not be able to recover files you are looking for.