@P12I was with one until I was put on a DSP earlier this year. Like @Ainjoule, I was using the while unemployed and I had pretty much the same experience. Underwhelmed and a high staff turn over. It really comes down to how good the person you are seeing at the time as to how helpful they are. To be fair, the one I was seeing when my health too a bad turn was really helpful it helping my through that and helping me apply for 3 month exemptions when I had treatments.
As for negotiating and advocating, the only thing the was ever said to me about that, was talking to an employer about a wage subsidy. Other than the lower mutual required obligations required from me, it was literally no change from when I was on the regular stream.