On Fixies... it doesn't bother me if they are built from scratch or purchased off the shelf. Either way, they make good sense.
All my bikes (nearly) have been bought off the shelfed and "customised" as time as gone on and parts have been worn out etc.
I've a Steel Pearson Hanzo and so far, I'm quite happy with it. With full narrow mudguards it weighs in at 9.6 kg. I'm sure by buying dropping the mudguards, buying a carbon fork, swapping out the handlebars and stem for lighter versions I could shave a kilo off that. Maybe more. It's not got the lightest wheels in the world either.
If weight is your primary concern, the Cartouche doesn't look like great value.
For bling however, it's a different matter.