What is actually different?
Dext does one thing extremely well: it reads receipts, bills and statements and pushes clean data into Xero, QuickBooks or Sage. It is a specialist, and specialists are usually better at their one thing.
Bizzle reads documents too, but as part of the same system that holds the ledger, so there is no push step and no sync to go wrong. The document, the transaction and the journal are one record rather than three joined by an integration.
So this is not really a like-for-like fight. It is Dext plus an accounting product plus whatever chases your invoices, against one system that does all of it slightly less specialistically.