I have stretch marks. I want to know if Rejuvapen would work on my stretchmarks? (Photo)

you need a combination of procedures to get the best result.  Please see a cosmetic dermatologist with experience.  Best, Dr. Emer.

Micro-needling motorized devices are basically the same.  Variables include the number of needles per head piece, the depth of needling and the speed setting.  Adding platelet rich plasma to the skin prior to the procedure should improve results.  Several sessions (usually more than two) are required to produce noticeable results albeit subtle. 
Stretch marks that are deeper require more aggressive treatments which may include but are not limited to resurfacing LASER, radio-frequency treatments and fat, Bellafill, or Sculptra injections.
.Please consult in person with an experienced Board Certified Plastic Surgeon prior to making treatment decisions.The cheap is cheap and one usually gets what they pay for.

The dermapen is minor wounding process and is not every effective.For a greater than 50 percent long term improvement I recommend Carboxytherapy with the heated Carbossi unit.There is no downtime and treatments are at 150 per session.You should reach maximum improvement in six sessions or less which can be stretch out if necessary.