I understand both. Each has it's pro's & con's. I went with what works best for us. I went with an ARE MX series cap. No windows except in the very front. Body colored win-doors on the sides & back. Dual handles/locks on each. Toolbox on d-side only. Full LED lighting, carpeted interior, cloths hanger, Yakima roof rack, 3-12v power outlets. Yup, it was stupid expensive. Yup, it does everything we wanted. It still does not leak but also has never been taken off either. I built my own 2 tiered bedslide. It works great but yeah, it is redneck-ish to be sure. I went with a self built bedslide for the following reason.
I asked a Contractor at HDepot, who pulled up in a brand new Ram 3500 with a brand new SpaceKap on it, about the BedGlide bedslide. He said to be careful of what you buy. He said a contractor friend of his bought a brand new one, from an authorized dealer, had it installed at that authorized dealer. It was rated at 2000 lbs. They put a pallet that weighed 1480 lbs on it, carefully with a fork lift, in the center of it, & it bent. The ultimate outcome was that the company said it was NOT evenly distributed & refused to cover it under warranty. I would NOT be a happy camper if that happened to me. Those things are uber expensive. If mine ever breaks or fails I am only out a few hundred dollars vs a few thousand & more for the install.