There is one accessory de rigueur with both skinny jeans on the streets of Shoreditch and an orange jumpsuit and black hood in the searing heat of Guantánamo Bay. The latest WikiLeaks dump has revealed that a disproportionate number of terrorism suspects in America's most notorious prison were apprehended wearing a Casio F-91W, a plastic digital watch you can buy for £8.99 from Argos. Beloved of hipsters and jihadis alike, the model has a rare and divergent customer loyalty that suggests we are in the realm of great design. But are these latest revelations the kiss of death for Casio or marketing gold?

The Casio F-91W was launched in 1991 and remains unchanged 20 years later. Since the 1974 launch of its first wristwatch, the Casiotron, this Japanese calculator maker has come to dominate the digital watch market, rebranding the conventional timepiece as an "information device for the wrist". Casios famously include not only stopwatches and alarm clocks but calculators and calendars. Their calculator versions, with fiendishly small buttons, epitomised the Japanese passion for miniaturisation. But the F-91W was a simpler model, stripped back both in its form and its multifunctionality.

That simple form no doubt accounts for its enduring popularity. In an age when the technological convergence of the "information device" has migrated to the smartphone, the watch is something of an anachronism, worn as much as a fashion statement or status symbol as for its time-telling properties.

The F-91W features the classic seven-segment numerical display on a grey LCD screen. It's a trusty timepiece: water-resistant, extremely durable and accurate to within 30 seconds a month. And while it is possible to buy luxury watches at 10,000 times the price that tick with atomic accuracy, doing so for precision reasons is functionalist logic taken to its absurd extreme.

By contrast, the F-91W's popularity with the young, cool set follows a converse logic that is no less a form of snobbery. On the one hand, the model is consistent with a diehard 80s revivalism, the wrist-based equivalent of a pair of Ray–Bans and a taste for Kraftwerk – and, yes, there is even the requisite touch of irony in sporting a 20-year-old digital watch alongside an iPhone 4. But it's more than that: unlike supplicants in the temple of the luxury Swiss watch, hipsters treat their ability to pull off cheapness as a mark of sartorial confidence.

What, then, do terrorists see in this watch? With 28 inmates of Guantánamo found to have had one in their possession, the F-91W and its metallic twin, the A168WA, were described earlier this week as "the sign of al-Qaida". According to testimony given by one prisoner, the model was useful because it was water-resistant: Muslims wash their arms up to their elbows before prayers. Another, more hapless inmate cited the built-in compass that enabled him to pray towards Mecca. His interrogators will have smelled a rat: there is no compass in an F-91W.

In fact, the model is al-Qaida's equipment of choice as the timing device for improvised exploding devices (IEDs). They're handed out in terrorist training camps, where junior jihadis learn how to wire them up to a circuit board, a couple of 9V batteries and a wodge of plastic explosive. This nasty package is concealed in a standard electrical outlet box, with the F-91W a macabre calling card – programmable up to 23 hours, 59 minutes and 59 seconds, it allows the bombers to put ample distance between themselves and their targets. In truth any cheap, reliable digital watch would do, and it may be an accident of fate that led to the F-91W gaining notoriety: some flunky gets packed off to an electronics shop in Peshawar to bulk-buy cheap digital watches, likes the blue rim around the face of that Casio number and lumps a donkey-load of them over the Afghan border.

When I approached Casio's PR team for some information about their bestselling model, I got a curt email response saying: "Casio is not making any further comment on the F-91W watch at this point in time." Is this a case of too much negative publicity? Is the fact that Osama Bin Laden himself wears an F-91W bad for the brand's street cred? Yes and no. Arguably, it is a ringing endorsement of the product's lethal reliability. Many brands would embrace that cult status.

All of this is a colourful distraction from what is truly remarkable about the F-91W – the fact that it is a digital product that has remained unchanged for 20 years. How many other devices can we say that of, apart from the even more anachronistic calculator? Casio's mainstay comes from a parallel world where designed obsolescence – the sales strategy that has cursed everything from our lightbulbs to our computers – doesn't exist. We desire no improvements or embellishments: it just works. In that first flush of affordable consumer electronics, I'm sure no one dreamed that in two decades the F-91W would still be popular and still relevant – just as in the 1990s, when futurists thought videophones were just around the corner, no one imagined a technology as archaic as texting would take off. We are intoxicated by technological potential, but it's the primitive devices we reward with longevity.

Should we – in solidarity with those Guantánamo inmates who are innocent, and in the spirit of resistance to an illegal detention centre – flock to Argos to buy Casios and flood the obtuse immigration counters of American airports with our F-91W-appointed wrists in an "I am digi-Spartacus" moment? No thanks – life looks a lot better through a pair of retro Ray-Bans than it does through a black hood.