A favorite instrument is the Suzuki Humming Tremolo. One can get them in all keys major and minor from The Musician's Webstore in Canada, and in the U.K., Harmonicas Direct and The Harmonica Company. Over time it has become clear that the Suzuki Humming is considerably more physically durable than the Echo Celeste, and it is also more precise and repeatable in note and tone. The price difference is very significant, however; Echo Celeste is much less expensive. I can heartily recommend starting out with Echo Celeste, and then if you are playing hard enough that they wear out, replace with Suzuki Humming if/as you can afford them! There is also the Suzuki Humming Mate, a smaller variety of Suzuki Humming; Alejandro M has reported that these too are excellent.
The Swan Professional is a startling newcomer. Good tone, strong construction, very low price. I have purchased them at Tmart, and friends on the Forum have purchased them from the Swan company's new outlet in the U.S.A. and reported excellent service. I think I slightly remember seeing this site in Chinese and wondering; perhaps I need to apologize for being linguistically challenged ☺ I do have to wonder how many of the other companies understand what Swan is producing. I think Suzuki has a clue; Suzuki Hummings are recently far more available in all keys major and minor than ever before. But the Swan Professional appears to be either almost as durable or just as, and prices much lower. More on this as experiences and reports accumulate!
The Hohner Echo Celeste still ranks well. Many positive reports have been received. Its tone quality is possibly the best in a non-wood comb. It has a very sweet tone, less volume than many, but great in heart. There have been some very less-then-positive reports; current theory is that there have been very rare bad runs of Hohner's mills for the Celeste. If you would like to try one, a very good source is Coast To Coast Music. The Echo Celeste is available in all major keys. Multiple reports have come in stating that if you ever do run into a bad one, Hohner will replace it cheerfully and quickly.
And we have the excellent and longstanding Tombo 1521, and Tombo 3121. The Tombo 3121 is available in all major keys and two minor; the Tombo 1521 is much more expensive, but with very good quality. You can find Tombo 3121, and Tombo 1521 Deluxe, from Harmonicas Direct.
definitely soliciting other good sources of tremolos, in every