Re: 30% chance of failure?
The spectrum cassette interface was a major technological advance. The black and yellow stripes gave an indication of data transfer.
Not really. It was just a slight improvement over what came before on the ZX81 where the whole screen did that when you were loading a tape. It's just that the Speccy kept its text area clear when loading so you could have something displayed. And don't get me started on the ZX80!
On the acorn atom it sometimes took several attemps and a half hour later to realise you had not plugged the audio cable in.
A little unfair to compare the Atom with the Spectrum given the difference in age. The Spectrum's actual rivals were systems such as the BBC Micro and the various colour Commodore machines of the 8 bit era and each did its bit to overcome the problems of the older machines such as the Atom, the ZX8x series and the Pet.
They had that sorted by the time we moved onto the BBC Micro though. That was an elegant design for a tape interface for the time.