The Singapore-based service can be used on the web, and has apps for Android and iOS. From now on, when users sign in, they will be asked to select their default currency. In most cases, this will be the local fiat currency. However, it is possible to opt for bitcoin too.
If users on your list of balances use different currencies, the app lets you switch those balances to your local currency. Then you can get a clearer idea of what you are owed, and how much you owe to others.
BillPin also state in their blog post that they are increasing the speed of the app, but to expect some "funky stuff" along the way too. The latter warning is due to the fact that existing users will be updating their default currency, and so this will affect balances across the BillPin network. The BillPin developers (team Pincho) simply recommend that users "Just make your changes and give it a day or two to settle down".
From the looks of the app, all parties of a split bill need to be existing members of the service. Furthermore, BillPin does not handle payments for you. All transactions need to be manually recorded, and so this should be thought of as a social ledger, rather than a payment transfer system.