OK so I tried both HSBC PayMe and Octopus O! ePay over the last couple of days to see what these things are about:
HSBC ePay - Basically you link it with your Visa or Mastercard. You don't need to have any banking relationship with HSBC. You load the app by sucking money out of your visa/mc, you can send and receive money to anyone you want via whatsapp, sms, or facebook, then you can spit money back out to your Visa or MC. Also the person you send money to does not need to use the HSBC ePay app if they dont want. They get a whatsapp with a link to the money, they can choose to simply enter their 12 digit bank account number and the money goes straight to their bank. That's it really. A simple but powerful tool, nice interface.
Unfortunately it crashes a lot of the moment. The infrastructure guys at HSBC did not expect the massive demand and their servers, firewalls, everything have overloaded and there's lots of weird error messages and bugs happening. I was eventually able to sign up and load it with cash from my SCB credit card, send money to a friend, but my friend couldn't receive it. I gave up and cancelled it. Hopefully these issues are sorted pretty quickly because it is a pretty nice app.
Octopus O! ePay - This one basically links with your octopus card rather than Visa/MC and it's a two way physical link with your octopus card. You don't really need any banking relationship with any bank at all (but you can if you want). I mean you can physically beep your normal octopus on the back of you phone to suck money out of the Octopus and load the app. You can also physically beep a normal octopus to spit money back out onto the octopus. For example, I used it to suck money out of my adult octopus that has AAVS, then spit it back out to my sons child octopus (AAVS not available for child octopus). So no more need to recharge my kids octopus at 7-11. I also paid a friend using this app too. Basically I physically beeped my octopus to sucked money out of it, sent it to my friend (both of us need to use the O epay app), then my friend can physically spit it back out to his octopus.
This O! ePay app only works like this with Androd phones. With iphone, the NFC is locked down to apple pay so blame apple for this. You can still use the app, but need to transfer money in and out by linking it to your bank account or charging at 7/11 by showing them your QR code. I actually have both android and iphone, so was able to load my account physically from octopus on android, and then see the balance on both iphone and android, pay my friend using whichever device I wanted.
I like both apps and can see uses for both. I have kind of ignored these mobile payment options until now but my eyes are starting to open and I can see a cashless future ahead . There is another app called JetcoPay but I havent bothered looking at this. Two is enough
I also use ApplePay and Android Pay. The difference with these is that they are commercial services, I mean you can use these in shops and restaurants. PayMe and ePay are personal peer to peer services, not for commercial use at this time. You can't pay your McDonalds burger with PayMe. But they are useful if you are in a group of friends and one person pays the bill with a credit card, you can pay your part of the bill using PayMe or ePay. It also appears as if you can earn double credit card points by doing this (one person paying the bill gets all the points, but everyone that pays them using PayMe or ePay also gets points when loading their apps).