grafted plants

 I just received an email from Suttons offering grafted plants, 'super productive'. But my experience is that extra vigour does not necessarily result in more crop, that the grafting process makes for a fortnight's delay in maturity of tomatoes, and that the incredibly high price (of 3 plants for £8 in this instance) makes it a deal worth avoiding.

Does anybody have experience of growing grafted plants where they have produced enough extra value to justify their cost?