Difficult question to answer really, without knowing a little more! Can I ask why you are contemplating this course and what you expect from it? That might help guide answers.

Many apologies David, my earlier response was eaten by gremlins. First of all cost - you should get an exemption from part of the diploma depending on how long ago you gained your NEBOSH fire cert. In turn, this will lower the cost and may swing it for you. Both the diploma and short courses will enhance your knowledge, your choice will be directed by whether you need a broad base of knowledge (diploma) or just specific knowledge in certain areas (short courses). The diploma aims to cover all the relevant areas that a fire safety manager would need to know, whereas short courses aim to provide specialist knowledge - possibly more in depth than the diploma. Something else to think of is that the diploma is delivered by distance learning. It is up to you to investigate, research and acquire knowledge. Also, keep an eye out for developments following the recent accreditation of the diploma courses by Derby University as a foundation degree. Just some thoughts for you to ponder, but drop me a line if you want to discuss this further. Regards, Jez