Think is, it quite an expensive option, if you think your going toneed at least a couple, in case one gets soiled. And as the baby grows you need to buy larger ones like you do clothes, where as blankets you only need the one lot for your cot.
Also I have read that they arn't very recomended for use with very young babies as its harder to control their tempreture as they are like a duvet, if your baby gets hot in the night or the temp drops its a lot harder to work around and small babies cant regulate their body temperatures very well. Its a lot easier to add or subtract a blanket in my opinion.