Revised review: 14Dec2013, reviewing Serial #52431. Thanks to Stephen Heape for giving me this second opportunity to review the Alexandre HR clarinet.
Barrel: 65mm; 52431 barrel is 62.2mm
Bore: 15mm, 52431 has 14.5mm bore
Key work: Sturdy key work, and very comfortable rings. They feel wider than normal.
Pads: Left hand mainly 9mm.
I have reviewed two of these and liked them both.
Why does the bell say “Paris” and below that say “Made in USA”?! My guess for the maker would be a late Pruefer product. The keys are unlike any French clarinet I have seen.
I would recommend using barrel rings on this horn, because one needs to pull out fairly far to be in tune.
However pulling out 3.15mm, as I did to test, is too far.
 For 52431 I only pulled 0.3mm at the barrel— even though this is a much shorter barrel! At the center tenon I pulled 1.2mm. So between the two models, I assume there was a change or variation in how long the LH keyed joint was made.
I now think that this was made by Thibouville/Masson. [That guess was from a long time ago. I now think that Thibouville may not have lasted into the 1950s and this is more likely a Malerne product.]
This is excellent intonation for a plastic clarinet. I'm guessing this was made around 1950.
 The low throat tones are not a problem on this model, which has a slightly different bore. If these were played softer they would be in tune.
I saw information on eBay that wooden Alexandre clarinets were highly regarded.
New information: I finally got one and it is reviewed here.
I'll be happy to work on Alexandre plastic clarinets again.  Yes!
These gradually widening side keys are rather unique.
The third finger ring seems especially wide.
These keys are seriously thick and sturdy.
 Boy, is that true!
Jan2010: I have just recently restored an Alexandre wooden clarinet, and I do not like it nearly as well as this hard rubber model.
[2013 #52431] Most appropriate for: Almost anyone, beginner to intermediate. Because of this clarinet being made of hard rubber, it has a very nice sound, keys able to withstand a beginner's rough treatment, and good intonation.