at your own risk
I am a audio Engineer major and I have some thoughts that might help you out. The air is a cool machine, no doubt. it is similar to the g4 which is still being used in some project studios that I am aware of. but there are quite a few things that I don't like about it, but that just means it is not for me. the only way I would suggest the air for any recording in garage band is if you were to use it just to record little riffs and only stuff to do a ruff draft. than transport it to your more powerful computer at home. the ssd would be a better option because they read faster, it is hard for a computer to record a good take with a hard drive that does not move as fast. I would like an air because I think that they are cool, but when i really look into the reality of that computer it is not for and audio engineer. You need to think if loosing two pounds is really worth the novelty of the worlds slimmest computer. for you to use the air to record you will also need to bring an interface, mic stand, microphone, guitar amp, no-matter what you need allot of stuff to get a good take, so I would save up and go for a MacBook Pro and have the flexibility over style, its 200 bucks more, two lb. more, and with good skill in the studio or on the go a sound that is really worth it.