I just joined this forum to give you guys my 2¢ and experience with the Predator 3500. I've also used this forum (in another thread) to help fix running issues, specifically the running rich problems. After purchasing the unit from Harbor Freight with the extended warranty on Memorial Day weekend of 2018, I completed the break-in process according to a mixture of things said on the web and from the Owners Manual. Soon afterwards, I removed the charcoal canister (information obtained from another thread on here) and replaced the spark plug with something better. The auto parts store was out of NGK spark plugs, so Autolite 63 it was.
This evening, I just changed the first Autolite 63 plug to another as my "Maintenance Time" light was on, it was time for an oil change, and the hour meter read 1009 hours. Yes, that Autolite 63 plug was used for about 800-900 hours and I have run my generator for more than 1000 hours. The only maintenance items I've completed on this generator have been, changing the oil after every 100 hours (only a couple of times was it longer, around 110/120 hours), changing the spark plug within the first 200 hours after the charcoal canister was removed, and cleaning the spark arrestor at the time of oil changes. I have run it with the spark arrestor and cone-shaped screen removed and found it was much louder and ran slightly better.
I'm pretty impressed with this unit, so far. I think that with anything, the proper and recommended maintenance goes a long way.