I generally agree with xLeitix's description of how you should approach your lecturer. I thought I would write an answer anyway to encourage you to speak up. I have encountered an unusual amount of bad lecturers and in my opinion it is always worth a try.
Venting your frustration to your professor is not going to lead to constructive change. As xLeitix said, giving concrete examples is the way to go. However, if your professor struggles with too much work load already or has lost their passion for teaching, take into consideration how much additional work this might mean for him. I found that approaches where the students display some initiative and willingness to learn usually work well and might even inspire change. Something like a group of students presenting the results for an exercise instead of the professor reading it off his answer sheet constructed 20 years ago. A student volunteer covering the review of the concepts covered in the last lesson, rather than listening to his repetition. Or his summarizing the last lecture with student input by asking them, that has the benefit of him knowing where the knowledge gaps might be.
Talking to some of your classmates might give you some more concrete ideas. I, for example, often made a list of topics people did not fully understand and asked if it might be possible to dedicate part of a lesson to repeat those. Talking to the other students can also directly benefit the class dynamics both in and outside of the lecture. Some of your classmates might have lost their motivation, or think they are stupid and the only ones struggling. A sense of belonging and being in this together could help all of you deal, even if the quality of the lectures won't improve.
The inconsistent notation might not be so easy to deal with, it takes a lot of effort on the professor's side, and maybe some unlearning of bad habits. One way of addressing this is being annoying and pointing it out during the lectures, something along the line of: excuse me, is X equivalent to Y mentioned in the textbook. This might antagonize the professor, but it will help the struggling students understand the lecture better.
Will there be negative consequences for you? Speaking up will make you more visible than other students which can lead to negative and positive consequences. I found that having the support of an other faculty member helps. I do not mean having a faculty member help deal with the under performing professor. What I mean is that in case your professor takes constructive criticism as an attack on his competence or person and retaliates, being able to rely on the support of another faculty member is incredibly helpful.
Having said that, I do not think that this is a very likely outcome in your case as you specifically mention that he is self aware of the problem and capable of teaching much better. You being a good student is also helpful, as no one can accuse you of making a fuss because you are about to fail the class.
I personally always found it worthwhile trying to improve the situation and helping the students that are not in a position to speak up for themselves.