Is it a bad idea to purchase older Apple routers?
I bought a second hand Airport Extreme (A1354) about a year ago for less than 50% of the price of a new one so my suggestion would be to do some good shopping around as they come up from time to time.

When I was looking for one, the minimum I was considering was the 3rd Generation (A1301) as it supported Dual Band. I would not personally buy anything older than this.

The model you are looking at supports Single 2.4 GHz or 5 GHz which means you can run either in 2.4 or 5 GHz mode, not both together. 2.4 GHz is the most commonly used wifi protocol (b/g/n) and means that the 13 channels available are very busy. 5 GHz (also n) is newer and less busy but not all devices support it. You don't mention which models of the iPhone, iPad, Macs etc you have but be aware that only the more recent devices support 5 GHz (iPhone 5 does). The newer devices support running both at once and communication is seamless between the devices.

The 4th generation (my model) also support the final version of N so I connect at up to 450 mbps which is great for transferring files. My Apple TV (3rd Gen) works great in a wireless configuration - mainly streaming data from my iMac (2011 - wireless) or Mac Pro (2008 - wired).

Apple has also spent a lot of time improving the antenna strength in the later models which really helps if you have a house with thick walls.

You can see a nice breakdown of what features are support by which model on Wikipedia. If you look further up the article there is a summary of what the improvements were in each model.

I received an update for my model within the last month, not bad for a product first produced in 2009 (I can't comment on older models as I don't have any).