The 8 foot led's that I have seen, I am not impressed. Some of them are made of plastic and they sag. I never have personally messed with them, it might be they come with center supports that whoever did it, did not install.
The 4ft's are more common and cheaper. I actually use the LED 4ft bulbs you can get at Walmart. They work very well and are cheap. I have installed hundreds of the great value Walmart 4ft bulbs, and in the past 10 years I have not had one fail. I had a vendor want to start selling me LED's wholesale, and I told him what I use and the price, and he said he could not match it.
You used to be able to get 8 ft lights that took 4, 4 ft bulbs and dual ballasts. That is the one thing about the Walmart bulbs, they are drop in and do require a ballast.
Now the Great Value LED screw in bulbs, that is a different story. I was buying the 60w equivalent, and I have had a lot of failures with those. So much so I stopped using them and started using the name brand bulbs that Walmart sells. They are GE or Phillips, I can't remember which. I am having better luck with those.
P.S. I am also impressed on how bright the walmart 4ft leds are.