I had my AGI prior to getting my CFI for this reason. During the beginning of the checkride, the examiner asked me to show him my FOI written. I told him I no longer had it as I had an AGI. I showed him the AGI, and he literally took about 20 pages of questions out of his binder of things to ask on the oral and threw it in the garbage. He was very happy to do this, as he said it cut out over 3 hours off the ground. All the questions he threw away were on FOIs. He told me that since I had my AGI, I was already an instructor, so he did not have to test me on any of the FOI knowledge, however he could if he chose to.

This was an FAA examiner, not a DPE.

Paying the extra $100 to take the AGI written was totally worth it to me in this case, but I have heard not all examiners do this.