The vanguard is made by daihatsu, which is owned by Toyota. Briggs partnered with them to make the engine. My father has a vanguard on his mower. Great engine. Any engine can malfunction. Mad Mackie is someone who has used the commercial turf engine on his mower and he seems to think its a good engine. I have read enough of his posts to believe he has a very good working knowledge of engines. As I said, I have no personal experience with the commercial turf engine, but I haven't read many bad reviews of them. I do have some experience with the els series. The ones with the flat air filters like on a car were not well designed and dirty air would by pass the filter when the plastic cover got hot and warped. B&s went back to the canister air filter with the last of the els engines, and it solved the problem. That's the engine on my friend's mower and it runs great. Doesn't use oil either. I am also a big fan of the kawasaki engine. I went with the fx series on my mower. However, the ones who have engine trouble on here usually use their mower more than a couple of hours a week. Residential owners usually don't stress a commercial mower enough to have too many problems. That is a great price for an is600 though. It would be worth looking at if the op can get one for that price. I have not found one in my area for under $6k.