I've used both of the two data recovery tools, my friend. Maybe I can give you some suggestions.
The first thing I want to say is, since your hard drive is corrupted, don't do any DIY attempts that may just make your situation worse. The corrupted hard drive means that there are some logic errors on the drive. In this situation, you have no other choice but to use the data recovery software to recover files from the corrupted external hard drive in a hurry, just as you've already been in consideration.
And as far as know, there's no absolutely free data recovery tool for corrupted external hard drive recovery. Some freeware is actually not free or has potential threats to your data or hard drive.
For your confusion, is Disk Drill safe, and which one is better? In a word, I've run both on my computer and not find any security issues yet. But iBoysoft Data Recovery is what I've learned about an Apple-trusted app.
For their differences:
- iBoysoft Data Recovery is stabler and quicker in lost data scanning while Disk Drill crashes during the file scanning process from time to time.
- Higher lost data recovery rate with iBoysoft Data Recovery.
- iBoysoft Data Recovery is more cost-effective.
- iBoysoft Data Recovery's support team responds to users' questions more quickly.
That's all my experience about them, you can free download iBoysoft Data Recovery for Mac to have a try.
By the way, if you want to go on using the corrupted external hard drive, you also need to fix it after data recovery. You can follow this article to get details: How to fix corrupted external hard drive on Mac?