For your money you get a decoder that can be picked up for £10 + p&p (Dapol Imperiums are rebadged LaisDCC) and it fitted to a model thats designed for easy DCC fitting.
You also get the added bonus that your new model gets removed from the packaging at Dapol HQ to have the decoder fitted, potentially damaging detail in the process then repacked to send to your or your retailer.