Redbook layer on SACD - good enough?

Buy it. No difference unless the manufacturer intentionally wanted to make one.

No. How could it? But it's likely that the mastering is different on the different disks--and there's no guarantee that the best version (or, rather, the one you would like best) is on one or the other. If both the CD and athe redbook layer of the SACD used the same master, they will likely sound identical.

DSD layer from SACD Hybrid wins over Redbook CDs. And more important is SACD being played on SACDP sounds lot better than DSD layer to be played on Redbook CDP at the same price range, or even more expensive.

This is a fact.

"And more important is SACD being played on SACDP sounds lot better than DSD layer to be played on Redbook CDP at the same price range, or even more expensive."

How do you play a DSD layer on a Redbook CDP?

Lafish: I've got SACDP some time before, and then discovered that mastering quality on available SACDs isn't as good as on good CDs (IMO), so I decided to get a good CDP instead. When SACD will be mastering with XRCD quality -then it won.
Kr4: is it common to manufacturers to make CD layer worse then SACD layer intentionally?