Can .5mm dermaroller be use on puffy under eyes, and will it get rid of puffy eye bags??

The average thickness of skin on the lower eyelid is 0.82 mm, so using a 0.5 mm dermaroller is too close to going through the skin and risking scarring and/or damage to underlying structures.I have my patients micro-needle their skin at home two to three times per week using a special hand-held device, the Livra Wand, that is manufactured by ProCell Therapies. It is not a dermaroller, as it uses a vertical "stamping motion" which gives a much more even pattern of vertical needle insertions into the skin as well as a more effective result. It also comes with disposable 0.25 mm needle tips for safer use.
My patients also combine home micro-needling with ProCell Therapies human growth factor serums. These serums are anti-inflammatory and are therefore more effective for reducing under eye puffiness.

Not a good idea. The very first thing is to find the CAUSE of eye bags. They can be due to fat herniation, loss of mid facial volume, overactive ocular muscles (Botox), and many other factors. Just derma rolling can make things worse. Find the cause, then match a treatment for eye bags- this may range from simple things like fillers, lasers, through to surgery for fat pad herniation. A specialist review is recommended. All the best, Dr Davin S. Lim. Brisbane Aesthetic Dermatologist.