I get a regular stream of contact forms asking if such and such bit of Multiblitz kit is a good buy at this price? Quite often I email back asking what is being bundled for their £/€/$ price as there is not hint of this in the initial contact form. The truth is I feel unless you're getting one of the relatively new units and it is bundled with quite a few modifiers it will have to be very very cheap. If you're already a Multiblitz user, then there is of course some justification for buying a lone head, but all the contacts so far have been from people who've never used Multiblitz lighting, so my advice will always be;
OK if it's cheap enough and comes with most of the accessories that will allow you to attempt the style of photography you're interested in & always check to see what new kit is available for the same price - better to own a new unit with full warranty & support than an old obsolete one!
I certainly wouldn't really recommend a beginner buy old Multiblitz equipment, then have to search out modifiers to suit, you almost have to willing to loose the money invested, as although I've always felt that Multiblitz are inherently reliable, spares and maintenance could be prohibitively expensive if not impossible depending on the age of the unit(s).
I recently bought a batch of 6 heads, all relatively modern, 4 had faults that rendered them only fit for spares as the cost of repairs would have far exceeded their valiue, so in the end I just salvaged the flash tubes that I could use. The 4 heads were put on eBay for spares at only a few pounds each, but in the end only one sold & the rest went to the local electronics recycling centre.
Born in 1956 (so getting on a bit now) I'm married and have two wonderful children we all live in Devon in the South West of England - on the Cornish border.