Ease of bulb replacement, and water proof endcaps. At the time when I set my T5 system up over my 29g bulbs were hard to come by, and I was using the regular endcaps. When I took my 29g down I never really thought about the lighting and let it sit out in my storage room, needless to say it had rusted to crap.....So when I set the 29g back up last week, I had VHO endcaps laying around, bulbs at my disposal, as compared to waiting for LFS to order the T5's. I don't have to replace my VHO but every 12-15 months though, I think your basing the 6 months on a magnetic, and not electric model. Also It might be just my silly eyeballs but the VHO's seem a little more intense.