My supply of working 880K floppy disks is dwindling rapidly and I was wondering whether it was worth it to invest in one of these or just try and find an 880K floppy supplier.
Depends on what you are storing on those disks. If you are planning on keeping important document on those discs and also are planning on keeping the files on the disks for a long time to come (we're talking years here)... well, then I would recommend a HD drive for use with HD floppies if you are running out of supply of DD floppies.
But... if what is stored on the disks isn't that important, more for everyday use, then I would recommend just using HD disks with your DD drive.
I have yet not seen one of my HD disks fail when being used with my DD drive in my A1200. And some of them holds files since some 10 years. I know there are people having problems with the data being easily corrupted when using HD floppies with a DD drive, but I am yet to experience that.