An accelerator here means a delivery pattern, not a licensed product. When a system shape recurs, so do its hard questions: how tenants or branches are isolated, where the audit trail sits, what happens to a half-finished transaction, which roles can approve what. Having answered those before does not give you a finished system. It removes several weeks of discovering them the expensive way.
The choice between this and a fully custom build is narrower than it sounds. The real question is how far your process differs from the ordinary version, and whether that difference is where you make your money. A difference that is incidental should be removed rather than encoded. A difference that is the business should be built properly and never squeezed into a package.
Three groups follow. They are ordered by who feels the change first: the people running the operation, the people selling and collecting, and the people using a product you own.