I have all of his instructionals. It's hard to say which one helped the most. The Back Attack series changed the way I think about about the back and demonstrated, to me anyway, many details about control that I hadn't considered. However, that said, I still do not get the back as often as I'd like. However, my armbar and triangle finishes have gone way up since watching these two series. The triangle series greatly improved my entries into the triangle and has me hitting them a few times a month now whereas before the best I could hope for was getting stacked. The armbar series for me was a godsend; My s-mount armbar had always been trash prior to this series and my armbar from the guard was laughable in my opinion. With the former I always felt too light and off balance - not in control. With the latter, I felt like my terrible flexibility meant I was ever only going to hit that technique on white belts. I don't feel that way anymore. I went from not even attempting armbars outside of drilling a month ago to hitting them on longtime blue belts. For me, that's a massive improvement. My armbars are tighter, with a much higher degree of control that offers a much smaller opportunity for escape than before.
Much has been said about Danaher's teaching style. Yes, it's repetitive. Yes, it's verbose. My solution was to download the digital copies from BJJ Fanatics and watch them on VLC Player. VLC has a playback speed slider bar where you can finely adjust the speed. I find that I can watch the videos 25% faster than normal without losing any of the details. A big positive, for me, with regard to his teaching style is that it seems to stay in my head without drilling. I am not super talented when it comes to BJJ. I can almost never recall the details of a new technique unless I've drilled it numerous times. Not so with Danaher, I haven't drilled any of the details I've learned in his instructionals but I've been hitting them in live rolls from memory because I can hear him in my head. For me, it just works. However, I can understand why he annoys so many people.