After playing tenor saxophone for almost 27 years now, I have never warmed up to a hard rubber mouthpiece and I had/have Brilhart, Meyer. Otto Link. Morgan, Yamaha and Yanagisawa and Vandoren. The only one I am using is the Vandoren Jumbo Java on loud electric gigs. Otherwise, I mainly use metal because it works with my anatomy. But the soloist design along with Aizen's improvements and secret sauce may make me move towards hard rubber.
The SO series with the 7* opening is like a Selmer H which is very hard to find. This should be 2.7 mm or .105 inch but the one I got is .104. This timbre and volume is even -- sax will never be even but it is even than most mouthpieces. I tried this on a 53 Selmer SBA, Yamaha YTS-62 and a 74 Buffet SDA. The Buffet is more spread by nature and this horns helps to focus that. Even at H or 7* it is relative free blowing. If you do descending arpeggios ending on the bell notes, this mouthpiece makes that easy and you will not break as much. Subtones usually end up with a lot of escaping air, but not on this one/ The horseshoe chamber is not as constricted as Selmer. The facing is perfect and the reeds seals properly.
Like I said wider tip soloists are hard to find and many retailers charge extra. ofr G and wider openings Thomann pricing is great and considering there is nothing else needed like a refacing - in the end this is a great deal.
Even at 7*, this still shows its classical roots. Push with faster air and/or softer reeds you can rock with this piece. Normal tone is jazz oriented.
The shank diameter is slightly large compared to most HR pieces , like Vandoren. But if you are flipping between and Otto LInk the shank diameter are comparable. Altissimo on this is rounder in tone than most and if you have the chops you can match timbre and you wont sound like you are doing altissimo. Y can do an edge of silence volume and a timbre like flautando on a violin.
I was once told that every horn player should have a soloist mouthpiece. This Aizen SO gets you a very playable soloist