Seeing as alot of cars are running close to 200bhp as standard with the DPF and without a remap, £1300 for a 20 to 25bhp gain seems alot of money to me.....
But if your DPF breaks and you need a new one you'll have to fork out that much for a new one anyway. It can be expensive but it's worth every penny. If it does block up it may effect other parts as well. My understanding is they are just for emission's..and anyway who said a bit of smoke will be a bag thing?