I purchased the RO150 and used it intensely for a particular project, then sold it afterwards. But loved it so much I bought an RO125 straight away for keeps.
Both the sanders take a tiny bit of getting used to in the aggressive mode. And the RO125 is a little trickier than the 150, but not to the extent that i would swap it out. The 125 is such a versatile sander it's mostly the only one I have with me.
Nearly a year into owning the 125 I have not noticed any change in it's handling/performance, suggesting no 'break in period' affect whatsoever.