It's brandable, if you search on Google FlowPro.com, Flow-Pro.com, FloPro.com, FlowPro.nl and FlowProInc.com all come up on the first page for a Flow Pro search. I don't think you will sell it to another domainer, you need to direct market or hope that somebody with an interest in Flow and Pro contacts you.
I regged several similar domains when the .pro restrictions were eased at the end of 2008, for example Jumbo.pro and Pronto.pro, the logic was Jumbo and Pronto are popular branding words, Pro is a branding suffix, and O followed by O sounds catchy. You could use the domains for anything big or fast so they have alot of possible uses. Again, I wouldn't be able to sell to somebody on NP, but if somebody looked up either word on Sedo, the Pro branding and rhyming angle would stand out.