These two jobs taught me valuable lessons (first hand). Worth a lot more than the ~$5,000 in time/wear/broken teeth cost me.
Fortunately, I used the crew day pricing tool and bid them ok even with the losses. Both jobs ended well and the land owners loved the result, it just cost time and frustration on my end.
Rocky land is a lot harder on equipment than first thought. It threatens to remove your tracks at every turn (literally). I had to slow production from 1.5 acre/day to .75-1 acre/day. Ten seconds of inattention and my 275 walked out of a track (thought I had everything to put it back on but spent 2 hours chasing the right tools, stubby bottle jack and 6' pry bars). Even going slow and skimming most of the ground I knocked out two teeth (carbide) in the last hour of the job.
The Douglas Hawthorn (thorn tree) is a beast. The mulcher rips foot long strips instead of chips. It bogs the head constantly, slowing production to 0.5 acres/day. It hides how big it is with wide spreading branches that cover a 30' diameter shielding from view the eight or nine trunks lurking inside,scheming to steal your time.
I have now updated my estimate algorithm to include a "surcharge" for rocky ground and or thorn trees.
Thorn trees will get knives instead of carbide. Hopefully that will increase production rate and the charge will cover the swapping of teeth.