from my research, here is what I've found:
1- The govt insists the payments be done on their national backbone, which works on 0 markup, so companies have to find different avenues for revenue
2- The device is essentially a mobile phone with no display(newest version has a small pocket-calculator sized lcd, but most do not) and just four buttons: power, volume up, volume down, and repeat last message. It takes a SIM and has a rechargeable battery and a loud speaker.
3- This means essentially operators a renting a very specialised "dumb-phone"; one which has a simple audio output but no input (and thus access) to the actual app. They can leave this "phone" out in the public, while keeping their smartphone separate and secluded.
4- The device rent is lowered or even waived if you have a high-enough transaction volume. So for people who have a low usage, they can stick with checking their phone; for people with more frequent usage, it pays for it self.
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I see a lot of benefits for this. AFAIK, each device is keyed to the user, so stealing it not beneficial, but even if some one did, no can use it to access the app or your funds, since all it does is receive confirmation SMS.
There no training involved, and more importantly, no handover of a device anytime you to step away from a counter; anyone can take over and just listen to the confirmation message.
one benefit the article mentioned is that people would dupe the seller by showing fake screenshots of a transaction, how that was eliminated by the device; no sound message, no payment.
But the best benefit is the multi-tasking; you can use your hands and eyes to keep focused on the task at hand while using your ears to keep track of payments. Imagine a food-stall seller having to wipe their grease/sauce covered hands and fiddle with a slippery phone, anytime a customer paid, it would never work.