Hi SRS,
How are you doing?
I am an SAP Product Support Consultant for SPP. There is no issues with the SPP module. Actually, it is always growing. SPP is even available in the Customer Connection program from SAP which gives the customers the option to request improvements in the application.
Regarding DRP: it is the same algorithm as MRP adopted to support the BoD (Bill of Distribution). The BoD is a Master Data in the SPP module which is a hierarchy of locations. The parent location (in the top) is the entry location for receiving procured materials. Furthermore the goods are distributed along the BoD to the child locations (level 2 and 3 below the parent). When DRP is planning, it rolls up the demands of all locations within the BoD to the parent location. The procurement is then planned and afterwards disaggregated to the child locations of the BoD.
I hope this helps to clarify your doubts.
Cheers,
Rodrigo