The other tool reads all 720 sectors and after each sector it verifies whether the pattern is (still) there. If not the screen turns black.

That's all what the tools do. But it was rather interesting.

I have several types of HD floppy disks and I found out that I have one batch of one brand that does actually work good.
The others fail.

I have an older batch of MEMOREX HD floppy disks. The label (with a RED memorex LOGO) sais: MEMOREX 5420 5.25" 2 S/ 4 D and there is also a "10" on the label. These disks work perfect in my 1050. (And yes... I have other prove of that, read on!) The magnetic foil is not as dark as other brand HD floppy disks I have. These disks also have a HUB ring. I also have a very special batch of the same memorex disks. These have darkgrey label. Also with the RED logo. Also 2s/4D printed on the label. These disks work fine too.

I also have a newer batch of MEMOREX HD floppy disks. These have a blue logo printed. The magnetic thing inside the floppy is more black. These disks don't have the HUB ring, and the label also reads 1.6mb. These disks refuse to work. So do also my BAS-F HD floppy disks and my 3M HD floppy disks.

Why am I rather sure the old batch memorex HD disks are good to use.

Well... the non-working batch of HD disks resulted in problems after only a few minutes (!). When I verified the disks just after writing the pattern, they gave no problem. But on the next verify I also heard the drive head having issues. And after another time, there showed up the problems.

The older Memorex disks kept giving good results.

Ok you would say now: but you wrote the test-tool YESTERDAY. How can you be so sure, the data on these disk will last longer.

RIGHT! That was the same thing I thought and said to myself. So I went searching in my floppy disk collection.

And what did I found! YES! I found 6 floppy disks of these OLD Memorex Batch which I used 3 years ago when I was creating a nice floppy box (that was a time I really want to go retro, and only use floppy and tape, in stead of blackbox, myide, sio2ide etc).
I found several games, and... (VERY interesting) a dual sided MEMOREX HD Floppy disk with NUMEN on it.

I booted the disks... and I watched numen. NO problems.
I played the games on the memorex HD disks. NO problems.

Today I rechecked my test disks (with the pattern). They still verify VERY stable. From the first to the last track. No trouble.
Tried other 1050's no problem.

Ofcourse you'll never know. But that the disks DO work after 3 years, and that with my test results described above (and especially when you also look at the test results of the non-working HD disks) I'm pretty sure these disks are safe to use.

One more thing:
First I thought it is the WRITING that is the problem. But I believe now that is not really the problem. All the disks that failed, do still carry the right pattern. After re-reading failing sectors several times, I get the RIGHT pattern on the screen. The recording of the data is probably too weak to read right.

I found out that my happy drives do have less problems. Perhaps because they read tracks in stead of sectors? I have no idea.