Flatbar racer or SS for kids/commute

allezoops

So, I've been advised not to put a Hamax on my 2010 Spec Allez Comp so [sigh] have to buy another bike...

My budget is £500ish, the question is, should I go for a flatbar racer like the Scott Speedster S50 flatbar

http://www.evanscycles.com/products/scott/speedster-s50-flat-bar-triple-2011-road-bike-ec025506?query=scott%20speedster%20bike

or

a SS/Fixie like the Spec Langster

http://www.evanscycles.com/products/specialized/langster-2011-single-speed-road-bike-ec024961?query=langster

ordinarily I'd be going about a mile with my son in the seat to drop him off at the childminder and then about 7 miles to work, all fairly flat.

Part of what I've been wondering is if I buy a racer am i not just going to be bored on a bike that's not as good as my allez? If I went for the single speed at least it would be different, or would I quickly get bored of spinning all the way to work (there are a lot of traffic lights)

Cheers

Allezoops