I have used GigaRec for audio. Depending on the mechanics of the CD audio transport being used, it may or may not play at all. I had high-quality contemporary CD players that would not even recognize the discs; conversely, garden-variety Discman players that handled it without a hiccup. This soured me on the concept pretty quickly and I have not used it since.
GigaRec ignores the timing information in the pregroove and, in essence, makes its own, more densely packed spiral groove in order to get more data onto the same area. Reading a disc recorded in this way can push the pickup to its limits. This whole operation requires a drive that has very close mechanical tolerances and excellent pickup performance such as what Plextor was manufacturing at the time; when they made their own drives. Getting a skip-free playback on another device is hit or miss. If the disc plays, it will be at normal pitch - just as the occasional commercially pressed 80+ minute audio CD would (same concept).
The Red Book contained specs for playback tolerance on things like this, required to display the Compact Disc logo. There are 1980’s-vintage audio CD test discs (from Germany and Japan, of course) which actually test things like this, as well as error/dropout compensation with measured defects of increasing size, and the like.