I bought a General SE-6 (same as a Rhino SE-6) 20+ years ago. It's worked well for me even though it has hit numerous rocks and beat its way through countless gopher mounds. All I've ever had to do was keep it greased - until recently when it developed a vibration. My fault - I hadn't sharpened or otherwise maintained the blades - ever. So I bought a new set of blades which cured the vibration. Here's a shot of the old blades versus the new:
No idea why the blades wore the way they did, with all the serrations. But obviously they weren't cutting, they were just ripping.