I have 2 of the 600s and have had zero problems. I changed out the bulbs to Ushios, with the money I saved, and use the ones that shipped as backups. they sent MH bulbs too. I mounted the ballasts off the wall to help with air cooling.
Since there is a fan running in the grow room and these ballasts are air cooled with big heat sink housings, why not take advantage of that circulating air to cool them down and extend their lives? I would like to take credit for thinking of this but I saw it used at a hotel with some electronic equipment in a computer room and stole the good idea. The spacers are old TV cable bushing connectors, but you could use any sort of 1/2' to 1" tubing with drywall screws to mount the ballasts.