Being of a certain age,and being obsessive-compulsive, I have owned all of the above, meaning I have played and tried them all, many for lengthy periods.I have found the differences, and can qualify them. But in the total sense ,the differences have been miniscule. I have also tested bells and barrels ,made from different and colorful and rare woods. I was especially moved by watching a well-known clarinetist in a large well-known Major Orchestra playing a long clarinet solo, with a barrel and bell made from brown wood. The most striking thing about his playing was the intonation, as colorful as was the wood. The Emporer has fewer and fewer clothes,and sales is the name of the game.
I can think of no more trying task for a student or for the parents or guardian of a student than purchasing an instrument, whether it be a new or used instrument.
Used is no more difficult than new, for very frequently you will be buying an instrument that is not completely adjusted for instant play or practice right out of the box. They are seldom in perfect adjustment, and the price you pay for new can be expontentially more and not worth the purchase much less the adjustment price you may have to pay, if there is no warranty which will be covered by the seller. And frequently the seller simply evaporates at least in service , especially if you are buying on that place, called the internet, an auction.
All or most auctions tell you CAVEAT EMPTOR, meaning buyer beware, and they mean it, those words, take them literally
Of course there are many many dealers of both used and new instruments that are completely reliable and many who will give you even more for your money that if you purchased new.
For instance, I once got a a cash allowance for a case that had come with an inoperable side latch.
And I once purchased a brand new Leblanc Sonata Clarinet for 269 dollars, from a pawn shop.
It had no case and came wrapped in enough plastic to wrap myself in, but after inwrapping, the horn played like and was a new instrument. Beautiful, and from a pawn shop, a business usually not associated with reliability.
Make sure you do not buy a cracked grenadilla instrument. It is a wonderful very hard wood and can be machined, but is also crackable, caused usually by rapid and extreme temperature changes. expensive to pin and repair. Price should be commensurate with condition.
However the rule remains, Caveat Emptor
I have also had the opposite happen: buying from a dealer, a representative of the manufacturer, and receiving a clarinet that was adjusted improperly, and even was defective, by my standards.
Now, this is doubly dangerous: if you buy on an auction, you know the biggest auction, and you don’t like what you have purchased, then you complain to the auctioneer, not to the manufacturer, so kiss your new money goodbye.
My best advice, have a clarinetist aid you in your choice and pay then for their advice.
Used instruments can be excellent. Any used Leblanc (Paris) instrument is very good, to excellent, never bad.
Almost the same for Selmer (Paris).
Yamaha wooden instruments using numbers 52-62-72-82 are professional level and are clones of buffets, but better in tune. Even the Nikkan Gakki instruments, which was Yamaha prior to 1970 are very good, and yes, they are Buffet clones….good ones.
I have friends who have purchased other french-made instruments which they say are good, however I cannot vouch for them.
For English instruments, you may have to have a special mouthpiece, although the newer models can be quite good, though with commensurate price.
So, for the parent, get profesional advice, or for the student, the same. Many times a clarinetist will have horns he wishes to sell, and many times they are excellent. I had a student who purchased a Leblanc Opus II for 1000, a terrific instrument at a terrific price from a teacher. It is doubtful that a teacher will sell a bad horn to a student, for obvious reasons.
Good luck and play well.