OMS e-Book has been updated and FAQ updated
I must admit I'd either forgotten or didn't know this existed until Pritam Pabla (Thank you!) mentioned it today.
Its been updated recently which is good to see: https://gallery.technet.microsoft.com/Inside-the-Operations-2928e342
Also the OMS FAQ has been updated, which gives you a lot more insight on Nodes and Data: https://www.microsoft.com/en-us/cloud-platform/operations-management-suite-pricing