Invoice / Bill approval workflow app recommendation

Does anyone have any recommendations for apps they have used to automate purchase invoice approvals? We don't use PO's but we want to automate the process for getting invoices approved, coded and on the system. We currently use a very manual process of emailing each invoice to the approver, sometimes this will be multiple approvers. We then save the invoice and the approval as separate PDF documents that are attached to relevant QB record. I can see 'Approvalmax' and 'Ezzybills' are available apps in the UK, but wondered if anyone has experience of these or can recommend something they use?

Thanks