Will your budgeting features include:
Separation of bills and spending money
Stopping you from transferring money from bills pot to spending
Ability to set monthly weekly or daily withdrawal/spending limits, and make it difficult to change these at short notice
Ability to block online gambling transactions (and betting shop/casino transactions if possible), and make it difficult to change this at short notice.
Reason I ask is that in my job I support people with addictions who cannot control their spending. For them encouragement to budget is not enough. They need barriers to actually prevent them choosing to spend too much money.
Also are you planning any service or transaction charges as part of your model?