The Yamaha YFL-221 flute and the Yamaha YFL-222 flute actually have very few differences. They are high quality beginner flutes with great sound and a beautiful exterior.
These flutes are in the key of C. They are made out of nickel silver and have a beautiful silver-plated finish. The mouthpiece is undercut and has a beveled embouchure hole, making it easier to create a clean, crisp sound.
The keys on both of these versions look great and are designed for beginners. The design is closed hole (or plateau) which makes it easier to play. They are also nickel silver and power forged keys. The bumpers are neoprene key bumpers, which are more durable and stronger than cork. They also have the offset G, typical for beginner flutes.
Both versions come with a durable plastic carry case.
The main difference is an added feature to the Yamaha YFL-222 flute. They have pointed key arms on the non-fingered keys. This adds beauty as well as strength to the keys. This feature is similar to higher-end Yamaha flutes.
Another difference regards the price tag. The YFL-222 is a newer version, so naturally the list price is a little higher. These are listed in the $800 to $1000 range. However, it appears the YFL-221 flute may be discontinued. You may be able to snatch up the YFL-221 at a good sale price before they're gone.
Both of the Yamaha YFL-221 Flute and the Yamaha YFL-222 Flute are great instruments. They are very similar, with one added feature to the YFL-222. If you are looking for a high quality, Yamaha student flute, but at a lower price, I would recommend purchasing a YFL-221 before they are gone. When they run out, the YFL-222 is just as good if not a better option - it just might cost a little more.