As a university student in 199mumble I had a side gig as the (freelance) technical writer for Amstrad Action - the magazine that pioneered covertapes, as explained in the article. The actual writing was easy and I could do it in my sleep: mostly answering readers' questions about printers, or reviewing the few applications still being released for the Amstrad CPC.
But I also put together the covertapes. And that was _hard_.
The main drawback is that I was very lucky if I got a master tape of the game. Mostly I just got a standard retail copy. That meant it invariably had copy-protection on of some sort... and I'd have to decrypt that to make a new master for Future Publishing to send to their duplicators (Ablex Audio Video). Fortunately I knew a couple of the best "crackers" working on the CPC, and I wasn't entirely a slouch myself, but even then it was a bunch of unnecessary effort.
As AA neared its end, the editorial team gave me a bit extra to not only produce the cover tape, but to commission the software on it as well. Occasionally I'd turn up a winner. A friend of a friend at university turned out to know the author of Chuckie Egg, the all-time classic 8-bit platform game, so I got that pretty easily. (Without copy protection!) That was a good moment. But often it'd just be some less than impressive game from the late 80s that hadn't sold particularly well first time round.
And as the article alludes, there were inevitably bugs. Finding out, after 10,000 copies of a tape have been duplicated, that it won't work properly on one of the three models of CPC... that wasn't a great moment. Ah well. We printed a bugfix in the next issue. Tapes were sufficiently unreliable that I suspect half the users just thought there was a loading error anyway.