I've never used or even seen a KiloTT but they have a solid reputation for being well priced for what you get and for being a reliable bike. You don't need to be messing about with a problem bike so my recommendation is to buy a KiloTT and go from there. Avoid buying cheap because those bikes don't last. 100 miles isn't enough to judge a bike, you need to judge it after a few thousand miles - sadly, most people recommending the el-cheapos do not have that experience with the bike.

Riding your bike (or any form of exercise) is not going to lose you weight on its own. You need to combine cycling with a good diet, only then will you lose weight. However, to keep that weight off, your cycling needs to become part of your life ie, not something you do as 'training', because if it's not, you'll not do it if it becomes too hard eg, cold and wet. Commuting, either the full distance or drive part way and ride the rest, is a brilliant way of achieving this. Finally, you need a bike you love to ride. If you don't like it, you won't ride it. If a particular bike is not your first choice, you're more likely to pass because it's cold or wet or hot. Commute on the bike you automatically go to and maintain a healthy diet, and you will lose weight and likely keep it off because what you are doing is sustainable. Interestingly, your commuter, the bike you sit on every day through all sorts of horrid weather, rubbish roads and homicidal traffic, may well prove to be a different bike to the one you ride on weekends.