1. They will never crack. You can play them inside, outside, in the heat, in freezing weather, and they will not crack.
2. The bore will not change significantly over time (unless you drop it), and they last much longer than wood. In my test of the four clarinets, I am comparing a metal clarinet from the 1930s with a clarinet from the 1990s. It would be very interesting to compare a metal clarinet and a wooden clarinet that are both from the 1930s. Unless the wooden clarinet has been kept in a perfect, stable environment, a clarinet from the 1930s is not likely to be a great instrument.
3. Metal clarinets save trees. I have heard many people report that good wood for clarinets is getting harder and harder to find. Most wooden clarinets come from the Mpingo tree which grows in Africa. While the tree is not likely to become extinct, it is quite possible that it will soon become what is called “commercially extinct.” In other words, there will be no good wood worthy of making a clarinet. The trees are not very large, and they take many years to grow to maturity.
The Mpingo Conservation Project has a very interesting and informative website with information about the Mpingo trees and clarinets.
4. They look really cool. This one is just my opinion and I’m always fascinated by old, nostalgic stuff, but silver and gold clarinets really look great. See the pictures of my Silva-Bet and my Cleveland clarinet.
The only disadvantage that I find is pitch, but again, this problem is on instruments that were made almost 80 years ago. I have been told that it is not possible to undercut the tone-holes of metal clarinets, but I’m sure that there is some way around that.
A problem with the Silva-Bet is that as I warm-up on it, the pitch change is drastic. Going from cold to warm, I have to pull out about 3mm or more. This causes problems because the relative pitch changes from the place when the barrel is “pushed-in” and when it’s “pulled-out.” When the barrel is pushed-in, the throat tones are sharp, but when it is pulled-out, the throat tones are a bit flat. This situation can probably be adjusted with different barrels, though -- we all use different length and dimension barrels on wood clarinets, too. Some of the later Silver Kings came with two different barrels. Unfortunately, I have not been able to try one out yet.
A brief history of metal clarinets
The Metal Clarinet Test
My experiences with metal clarinets
My thoughts and opinions on metal clarinets
More info and pictures of the Silva-Bet used in the recordings
More info and pictures of the Cleveland used in the recordings