We have been having a similar discussion on recorders.ning. The Zen-On is 440, I believe.
I would NOT recommend the G-1A. I sent mine to a friend who has the 1500B and he compared them (he has been playing for over 40 years). The newer one is not better, according to him. It is worse. I haven’t played the 1500B yet, but I have played the G-1A. It is not good. I have ordered the 1500B from Early Music Shop (http://www.earlymusicshop.com/product.aspx/en-GB/1002725-zen-on-bressan-alto-model-1500b-plain). It is costing me about $63 because it is coming from London.
I also have the Yamaha Ecodear, which I like a lot. The Yamahas, however, seem a tad sharp (as in cutting, not in tuning), but the Ecodear is more mellow to my hearing. I have the Aulos Haka Alto which I have just gotten and it is nice, too.
I considered the Bernolin, and I am sure it is nice, but it is just too much for me to spend on a resin recorder. Now, if I get really good in the future, maybe.
Take what I say with caution as I am fairly new to this. But, my friend has a lot of experience and I trust his expertise.