Regarding Magnum Steno theory. There are several reasons I like this theory. One of which is the huge dictionary you get which is over 310,000 entries.
I have ended up writing quite a long response so I've broken it down into sections.
Writing Short:
The biggest reason I like it is its ability for the stenographer to "write short". This means writing as few strokes as possible. For example, writing the sentence: "They are going to have to hear what you have to say".
Here is that sentence written in various theories.
Phoenix: (8 strokes)
THA*EUR / TKPWOEG / TAO*FB / TAO / HAER / WHAUT / KWRO*UFB / TAO*S
StenEd (7 strokes):
THER / TKPWOEUPBG / TOF / TO / HAER / WHAUF / TOBZ
Plover (8 strokes):
THE / R / TKPW*G / STRO / HAER / WHAU / STRO / SAEU
Magnum (4 strokes):
TH*EFRGT / TOFRPL / WHA*UF / TOS
In the Phoenix example I gave the shortest possible way to write that sentence which included some phrases such as "they are" and "you have". Some phoenix students insist on writing everything out including putting "-ing" endings on in a separate stroke. If this rule was applied, the Phoenix version would be 13 strokes: THAEU / R / TKPWOE / -G / TAO / SR / TAO / HAER / WHAUT / KWROU / SR / TAO / SAEU
In the Magnum example, the phrase "They are going to have" is written in one stroke which can be broken down like this:
They : THE
are : -R
going : -G
to: -T
have : *F (V)
Therefore all put together that makes "TH*EFRGT". You probably won't be able to piece this together while on the job so you have to learn it beforehand. Therefore, Magnum steno can take longer to learn than some of the others.
However, as a student, you don't have to learn that brief if you don't want to. You could equally write it out like this:
THE / R / TKPW-G / TO / SR
For me, I'd write it like this:
Combine "they are" into one stroke "THER"
Add the -T key to "going" to make "going to": "TKPW-GT"
SR: have
I'd write the entire sentence in 6 strokes and without having to rack my brain to remember a phrase.
Phrases:
As you can see above, there are a lot of phrases built into Magnum Steno and the words are usually pieced together in a logical way. I really like this "phrase building". Here are some simple examples:
I = EU
You = U
They = THE
Want = -PT
Need = -FRB
Were = -RP
Think = *NK
Know = *N
You can combine these in any way to make "I want" (EUPT), "You think" (*UNK), "They know" (TH*EN) etc..
Shortcuts:
Magnum has all sorts of shortcuts built in which help you write short.
dis / des can be contracted into "SD". "Decide" = SDAOEUD. "Disown" = SDOEN.
conf / conv can be contracted into "KW". "Confer" = KWER. "Converge" = "KWERJ"
imp / imb / emp / emb contracted into "KPW". "Impact" = KPWAKT. "empower" = KPWOUR
and so on...
Speed above all else
Sometimes these phrases and shortcuts create conflicts with regular words. Most theories would keep the regular word as the normal stroke and either not include the shortcut, or relegate it to an asterisk stroke. However, Magnum puts the most commonly used one has the normal stroke, and the least used one as the asterisk stroke. For example:
"could you be" / "cube".
Most theories would have "cube" as the main stroke "KAOUB" and put the phrase as "KAO*UB". The problem with this is that other phrases of a similar format don't have conflicts. "would you be" (WAOUB), "could you have" (KAOUV). So traditional theories would have you remember that one of the phrases requires the asterisk. But which one?
Whereas Magnum realises that "could you be" is more common than "cube", so it puts it as its main stroke and puts "cube" as the asterisk stroke.
This means you need to remember which words have been relegated to an asterisk stroke, but I haven't found this too hard and the payoff is worth it.
This is what I meant by "less logical than the rest". I suppose what I really mean is "less consistent when writing normal words". Most theories would have full words as the main stroke. Briefs and phrases would never overrule a full word. So you can always know the correct stroke for a full word. However Magnum would have to remember which words are overruled and require an asterisk. Therefore it's not as consistent, but I do agree with the reasons for doing this.
Conclusion:
Ultimately I like Magnum Steno because it focuses on the "short" in shorthand. One of the reasons I decided to take the extra time to learn it as my theory is because I want to write fast one day, so if I'm already writing short, I will make it easier to write faster. When writing at normal pace, my fingers will be moving much slower than one who writes everything out without briefs or phrases.
I am in no way affiliated with the creator of the theory. I'm just a guy who learnt it and found it had everything he wanted in a steno theory.
I hope this helps :)
Mike