This Dell has strobing pixel refresh and pixel shift, two anti-image retention features. Zero image retention experienced so far.
Well I would hope you aren't having image retention (burn in) after a couple of days.
Though I don't see strobing refresh as burn in prevention. For the same perceptual brightness you end up doing similar damage. If you run at 50% duty cycle, then you need to run 200% brighter, so it's a wash.
But strobing should eliminate the Sample and Hold effect, for those that have a fetish about that.