Accepting ACH payments on larger client invoices (30-100k+) for a few dollars is why we use them at one company.

Is the experience sticky? Stripe supports ACH transfers, so I would assume it would be straightforward to build on top of Stripe to replicate bill.com’s functionality.

Their core business is more around invoicing, so i wouldn't say so.

No. Speciality is Accounts Payable which is quite a different business.

Recurly may be a more similar competitor