I haven't used a Hennessy, or even seen one close up, but anyway... While yu do get the complete package, I'd be worried that you don't have the flexibility that you get from a separate tarp / mozzie net. And lets face it, they're not cheap...
OK, if you go down the DD / Group Buy / etc route you need to get a tarp. But you can choose whatever tarp you like, from a cheapie surplus basha sheet to a monster Tatonka or Kathmandu tarp - and a tarp is a generally handy thing to have anyway, even if you're tent camping.
The DD in an encloseable hammock, so you don't actually
need a net unless you're going somewhere malarial, when you need to worry about the little b****rs drilling up through the hammock itself. And if you do get a net, you have the option of not using it - if there's not many midges around, I find the openess of not having a net much preferable.
I'm not knocking the Hennessy, I'm sure it's a great bit of kit.
And I would agree that if you're more than 6' tall or very heavily built, then the DD might be too small. TBH, I'm planning on replacing mine with a group buy hammock to get more space - but it was a good, cheap introduction to the world of hammocking.
Really, the best thing to do is to try and get along to one of the meets - then you can look at lots of different options, and maybe even try some of them out if you ask nicely.