German System versus Boehm System
You will sometimes find the expressions "Boehm" and "German" on lists of manufacturers of clarinets and reeds. There are differences in size, in sound and in price. What is this about?
As you are not German (in that case you would read the German version of this page) you probably will think that all clarinets are of the same design - and that the Boehm System is "the classical clarinet", since this type is used in nearly all orchestras in the world by nearly all top clarinet players - and one could leave it at that. BUT: It is not. In German speaking countries they use a different type of clarinet, the German system, or a special version of it, called Oehler system, which derives directly from the Müller clarinet (and not from Klosés Boehm System). You find the historical background under History.
Such development is rather normal for instruments: Some hundred years ago most larger countries had own systems for all types of musical instruments, but in a long process these were standardised. The Academy in Paris payed a central role here - so most instruments we play today are of french design; except for example the string base (where the German model dominates the world because it is much easier to play German/Austrian classical composers with it - and they make up most of the string bases repertoire: Bach, Mozart, Beethoven etc.). The same is not true for the clarinet systems:
What are the Differences?
Both instrument types look rather similar, the most obvious difference are the keys for the little finger: Where the Boehm System has four levers, the German system has two rather flat, half-round key ends that both have a small wooden roll for sliding.
In detail there are larger and smaller differences in the keys, the mechanic, the mouthpiece, the lay, the reed and the bore. Generally speaking the Boehm system produces a sharper, lighter sound, that is more flexible than the German system. The German system produces a darker sound on a much harder reed. But then even to professional conductors the sound is so similar they couldn't tell the difference by listening (sais Daniel Barenboim in an interview).
Technically and from a musical standpoint both systems are on the same quality level. Mechanically some details on the Boehm system make it easier to build and to maintain - e.g. where the German system has long levers, the Boehm clarinet has turn-keys that last longer and work more reliably.
You will find, too, that many Germans fix their reed with a string to the mouthpiece, a simple, perfect way (although the ligature was invented by the German Iwan Müller, too). But many Germans today use a ligature, too (it is quicker), and you could, if you knew how, fix your reed with a string, too. In case your ligature breaks it is a good thing to know how that is done.
Since the embouchure is generally somewhat different (Boehm Mouthpieces usually have a different lay, and use lighter reeds, and fingering is different for some tones, you can't easily switch between the systems. Nevertheless you can. But you should prepare to re-learn parts that you have already played hundreds of times (that really "burns in" in your brain) and you should avoid to mix systems; this usually makes it more difficult; that is: you should not buy a Boehm Bass Clarinet and continue to play a German system B flat at the same time.
Will the German System survive in the long run?
The main disadvantage today for the Germany system is the price: Since the Boehm clarinets are built in much larger numbers, instruments of similar quality cost about 50% to 70% of what is charged for the German model. There are, however, instrument builders in Germany that build German system instruments for the high end segment of the market in a quality that is not rivaled by anybody else in the world.
However, that is of hardly any meaning for the large number of amateurs. The effect is that today you find a growing number of Boehm systems with amateurs in Germany, while professional orchestras usually still will not accept players playing Boehm. This used to be true for the world's best classical orchestras (like the Berliner Philharmonics, Vienna Symphony - allthough I am not sure what it is like today).
I think that in the very long run - and be it for the lower price and the better maintainability - the German Oehler system will be used by an ever shrinking number of top professionals and the Boehm system may well become standard in Germany, too.