I have had the opportunity to work on both. I love the Flex for the correction and the Rupes is great at finishing. Simply both are needed, but Get the Flex and as soon as you can get the Rupes.
Contact the guys at Gtechniq and see if they have a "reason" for the spotting or a way to treat the spots. Sorry I could not be more help. I am in Texas too so I would love to see how you remedy this issue.