Hey there.
I only change the inserts if possible. I work in the automotive development industry. For safe, clean, and non-skittering wipers the inserts should be changed every three to four months. Really it depends upon various environmental factors, but that is the general rule of thumb.
Unfortunately the industry rarely employs the high end wiper inserts. They go for cheap and functional to improve prices and bottom lines.
Lexus however actually uses Valeo on their higher end models (LS) as the factory standard.
Soooo.
I am just wondering if anyone in the forums has tried the Valeos on a lowly ES like mine.
Didn't mean to be vague.