I have used Platinum 9.0 since it was released - and it is absolutely stable and reliable.

However - DO NOT - upgrade from 4.0 to 9.0 in the middle of your project.
I have used all versions (4-5-6-7-8 and 9) and the development has been great - and the difference between 4 and 9 is so big, that 9 will look and behave as a new editor - and somewhat confusing compared to 4. I.e. with version 7 we got the keyframes everywhere.

Also - in spite of the backwards compatibility there might be some problems for 9 to interpret the version 4 files correctly.

Finish your project in 4 and look forward to new experiences with the great version 9.0b