Amati Full-Boehm Clarinet
The Amati full Boehm model ACL 615 and the A-clarinet ACL 675 are available in Prague, and cost a lot less than other makers' offerings (though considerably more than when I bought mine, at present exchange rates). Details of ACL 615 or its successor should be available on the Amati website .
The differences between Full-Boehm and standard Boehm (French system) are:
1. The additional semitone in length, giving low Eb and also a very good alternative to the throat Bb. (Amati also offer a model without the semitone extension.)
2. The auxiliary Ab/Eb for the left hand little finger.
3. The articulated C#/G#; the hole being closed by any of the right hand ring keys, making certain trills and runs easier (as on a saxophone). There is also an additional C#/G# trill key for the right hand: this seems the least useful of all the extras.
4. A forked Eb/Bb is available for the left hand (fingers 1 and 3), and can be very useful.
Regarding item 3 above, this arrangement means that the only cup on the instrument that is not positively opened or positively closed is the C#G#. The pad may stick down, as it relies on a weak spring to open it. This fault is also common in saxophones. If this causes problems, put a piece of thin tissue under the pad before putting the instrument away after use.
For a more detailed and visual comparison of Standard and Full Boehm, click here.
The picture shows the additional keys. You might also notice the small hole underneath the lh Eb/Bb trill key; this is closed by ring lh2 (and therefore by any rh ring) but not by lh3, so that the forked Eb/Bb gets good tuning.
The only fingering difficulty I have found is in the positioning of the left hand little finger keys, this may be because lh3 ringed hole is less offset than on standard Boehm models. (This "difficulty" quickly evaporates if one is used to playing a number of different clarinets.)