The main issues with nerf bars are their construction, materials, and mounting method. My truck came from the original Texas owner with a set on it. One Iowa winter utterly destroyed them.
They were poorly constructed with plastic caps on the ends of the tubes. Those did not stay in place, and once lost, the uncoated inside of the cheap thinwall tubes rusted through faster than a tin bean can.
I'm going with full-length diamond tread aluminum running boards. Those will provide far better protection for my rocker panels as well as the rust-prone Dodge door bottoms than any nerf bar ever could. I plan to fabricate a frame mounted receiver-type system to mount them to avoid the whimpy strap and sheetmetal screw mounting. They will be very much like hidden nerf bars under the running boards and will allow for easy removal and will hold anyone.
Pay attention to how any nerfbar you choose mounts, too. If you're a big guy, you'll find they all have cheesy sheetmetal screw mounting and won't hold up. REAL nerfbars mount solidly to the frame and are intended to protect the body sides from tree and rock sideswipes when offroading. Huge difference in materials, too.
Spend your money wisely. Look for heavy gauge tubing, maybe stainless steel, and welded-on sealed endcaps at the very least. Examine the instruction sheet and mounting materials and picture how it will hold up to years of weather and use.