I own two plastic alto recorders: the Yamaha YRA-302BIII and the Aulos 509B "Symphony". In this review, I will compare the two recorders: I wondered for some time which of the two I should buy and a direct comparison such as this would have been helpful to me at the time.
In terms of build quality and finish, there is nothing to choose between the Yamaha and the Aulos. They are both extremely well-finished; the joints are tight; they both come in a decent protective case. They are both very attractive musical instruments.
Both recorders are easy to play, in all registers. Reaching the highest notes is not a problem on either recorder.
I have read adverse comments on the web about both of these recorders regarding their intonation. I would disregard these comments entirely. If you were to attempt to play every single note on *any* recorder using exactly the same breath pressure, you would find that some notes played out of tune. This is the nature of the instrument. It is up to the player to play an instrument well in tune by applying the correct amount of breath pressure to each note. Regardless of what you may read elsewhere, don't worry about the intonation of either of these instruments; you will have no trouble playing either the Yamaha or the Aulos in tune.
One difference between the two is that the windway of the Yamaha is somewhat narrower than that of the Aulos, which means that there is more resistance against your breath when you play the Yamaha. This also means that the Aulos sounds louder than the Yamaha - the wider windway means that you blow more air into the instrument. Neither is "better" than the other in this respect; but they do differ and you may prefer one over the other.
Volume aside, the Yamaha has a very different tone quality to the Aulos. In my opinion, the Yamaha sounds more refined and poised, whereas the Aulos sounds more robust and meaty. In terms of tone, I can't say that I prefer one over the other; they both have their merits and I enjoy the sound of them both.
I find that the Yamaha's narrow windway causes it to clog sooner than the Aulos and I do find this annoying. Of course, the Aulos clogs too, eventually. A quick suck clears the windway of condensation on either recorder and enables you to continue.
In conclusion, I would highly recommend either of these recorders. They are both excellent musical instruments and if you're in the market for a plastic alto recorder, I don't think you would regret buying either one. If I were forced to choose between these two recorders, it would not be an easy decision. I think that I would probably choose the Aulos over the Yamaha, mainly because it does not clog quite so readily. But then I would miss the delicate tone of the Yamaha...