What I can tell you as a grateful recipient of DBS from my own perspective is this.
I didn't want ....holes drilled in my skull, permanent brain damage, altered personality blah blah blah.
I had the surgery 10 yrs ago and my quality of life was going downhill rapidly.
I wanted it to improve which it did and I was willing to risk that as personally I felt there wasn't a great deal to lose.
18 months ago both batteries went flat and needed replacing and so I went just a few days with no stimulators working before surgeon could replace them and I realised then how dependant Ive become on the hardware implanted in my head!
Several yrs ago I became aware that studies were recording positive outcomes from DBS done earlier rather than later was preferable.
So thats it from my perspective.