SEPA instant will settle transactions 10 seconds. Drawbacks: banks can opt to participate, initially limited to 15k EUR, plus not obvious what the cost is. Banks are charged 1 EUR per transaction, so it'll be at least 1 EUR charged to customers.
The price of a transaction is as important as the speed, IMO.
Private transfers: instant transactions between individuals, no transaction fees. (Though I suspect internally they do the usual reconciliation between banks at the end of the day).
Business: instant transactions to your account from your customers. Yearly fee: 500 SEK ($61), price per transaction: 2 SEK ($0.24), price per reimbursed transaction: 2 SEK ($0.24)
There are also limits on how much money you can send in one go, but it's usually more than enough for individual transactions and for small businesses.
The price of a transaction is as important as the speed, IMO.