Back to your original question, I really don't see how the 1.6 GHz CPU wouldn't be enough for mails and browsing.
The only reason why I would even consider a 21.5" FHD model is if I really wanted an AIO running OS X but wouldn't have any requirements beyond that. Otherwise, there are either cheaper or better options available.
Don't need an AIO? Get a Mac Mini. Don't care about OS X? Get a PC. Having more requirements? Get a 27" or whatever is applicable.
Once you buy some upgrades, the price gets closer to the 27" models which offer much more versatility (and most likely resale value) which puts the 21.5" in an awkward market position. Either rather inferior hardware or paying a price for which you could almost have gotten quite a bit more.