I have a Vortex on my M4. It is over 5 years old. It has been ridden around in my trunk, front seat, and spent lots of time on the range. I have had no problem with it. I do not abuse my rifle, likewise I do not overly baby it. I think the Vortex looks much better, 'cooler' than the Phantom. As long as you take reasonable care, it should be no problem.
BTW-I use this rifle when teaching the departments tactical carbine/urban rifle course, so it gets a lot of range time.