You will get a better quality deliverable of your product on time. Being a Senior QA with 5+ years of experience, I care about client satisfaction and strictly adhere to the timelines.
I assure you if there is a defect leakage in the testing (unless it is a requirement gap, miscommunications, new enhancement, etc.), defect retest and E2E regression will be done without any charges.
As deliverables, you will get the QA signoff on the tested product, test plan, test cases, test result, Bug report, root cause analysis, and traceability matrix.