Danzan Ryu Jiu-Jitsu for self defense?

Classical jujitsu (such as Danzan Ryu) is an encyclopedia of techniques for grappling, striking, and weapons. How it is trained is typically by memorizing kata and performing it with a partner. Each kata is done in some formal, concrete way. That's usually thought of as the "demo" version of the technique. It usually doesn't work very well in most situations. Later on, the practitioner learns variations (henka) of it for each different situation. There can be a dozen variations for the same technique. This means that a kata syllabus of just 100 techniques can easily turn into thousands.

Partnered exercise in classical jujitsu typically happens with compliant partners who will do their part, stop, and let you do any number of things to him with little resistance.

In MMA, Brazilian Jiujitsu, wrestling of all kinds, sambo, judo, etc., it begins much the same way. You will have a partner and a technique you are learning to apply. Your partner will, at first, let you do the technique to him. This is just to learn the technique. Pretty soon after that, your partner will add resistance. When you can deal with added resistance, partners then try to do other things to you to make you aware of where you're vulnerable. They won't tell you what they're going to do. And finally, there's sparring (also known as "rolling") where you and your partner are doing things completely spontaneously, with neither of you knowing what's coming next.

Another thing to realize about classical jujitsu is that the kata were arranged into sections, but the sections were not necessarily organized in the most practical way.

Judo was an advancement over classical jujitsu. When you look at Judo, you'll see that they organize their throws into a taxonomy. In Judo, you learn each technique in a predetermined order. The order is important. The first handful of throws you learn will apply broadly in the most situations. The last throws you learn will apply in more specific situations. And so, a beginner in Judo can gain broadly practical skill in very little time. That was the idea anyway.

Brazilian Jiujitsu also organizes its techniques in a practical way, by the way. The things you learn in white belt are 90% of the techniques that you'll see in competition. It's because those techniques are the ones that have the highest rate of success in competition and which apply most broadly. They're considered "fundamental", because without them, you can't apply the techniques you learn later on.

Another thing to consider is safety. You can't do sparring if you've got broken fingers, you've got a crushed trachea, or your eyes have been poked out, etc. So there must be rules when sparring that everyone agrees to, and the rules should be there only to prevent injuries, rather than limiting what kinds of techniques can be done.

Classical jujitsu doesn't do sparring at all, because they have no rules set up to prevent injury. They believe that adding rules would hinder them from using techniques such as eye gouging that they consider too important not to practice. And so, they don't spar.

But without sparring, can anyone expect to learn reliable self-defense? The answer is no, and this has been proven many times before.

You can still learn the eye gouge, the fish hook, the trachea poke, etc. They're not exactly secret knowledge. But those techniques are far less important than the fundamental skills needed to be able to apply those techniques on a struggling opponent who's trying to do the same to you. You can't get those fundamental skills without sparring.

The biggest realization that came out of the UFC and similar MMA venues is that you perform the way you train. People that didn't train with others who were trying to grab them, throw them to the ground, wrestle, and choke them out were completely unprepared for it when it happened to them in competition.

It's been observed many times that even black belts in styles like karate, taekwondo, aikido, etc. often lose in fights in real life. It's because when they actually have to fight for real, they realize that none of their training prepared them for it. They're like a fish out of water. They don't know what to do. They can even freeze up in the fight.

Bottom line: It's how you train that matters, not the style.

So let me get back to your main question. You want practical self-defense and are trying to decide between classical jujitsu and BJJ or catch wrestling. The answer should be clear now. While classical jujitsu will give you a lot of interesting techniques, how they train is inferior to modern MMA, BJJ, and catch wrestling for the purpose of giving you a reliable means of defending yourself in real life.

Hope that helps.