Its one of those maybe it'll pay for itself, maybe it wont. Its not just the DSG that can be expensive to fix if it goes wrong - i seem to have read a lot of air con woes as well which is also expensive to fix
If its your main car or is used a lot then i'd go for it, the peace of mind it will give you will be worth it and at £265, thats only £20 a month, not really a lot when you think about it