Is the Chromebook Acer C720 a good buy?

Hi guys,

Is the Chromebook "Acer C720" (the 4GB ram model) a good buy? I currently have an iPad2 as my "go to device" at home when I just need to surf the web. I'm sure the chromebook can take on the iPad in this regard, but can it also replace my desktop?

I don't demand much of my desktop, but I do need to eventually run an audio editor (audacity), watch a FullHD movie and download torrents (utorrent). Will I be able to do that on a Chromebook?

I also need to make Skype calls, but I already know that it's currently impossible on Chromebook (I can live with Skype calls on my S3),

The thing is: I can spend $400 (max) on a "device" to replace my iPad2, that I use 99% of the time at home (I really don't need a device that I'll take outside with me). The Nexus 7 is not an option because I want a bigger screen. If possible, I'd also like to use that "device" to replace my old desktop. It's important to notice that I currently don't have a notebook because I never really needed one (I just use my phone "on the go" and the iPad at home. Eventually I'll also use my desktop for specific things, like I said before).

So.. I'd like your help to decide which one is a better option. Play safe and get a $400 used Notebook (i5 or better) running Windows on Ebay (wich is bigger and heavier than the other options, but also more powerful and versatile) a $400 Android Tablet (with a 9"+ screen) or the $250 Acer C720 chromebook (the 4Gb version is $250 at BestBuy)?