I have no knowledge of that flash but from the numbers it is not as powerfull as a sunpak 383.....not many flashes work at a distance of over 60 ft and that one claims 40 ft.
There are softwares that will reclaim details from the shadows...while they can not do miracles but they may surprise you at what they can reclaim.
Shadow/highlite tool in PS or fill flash tool in Elements and I am sure Paintshop also has one.
There are also stand alone applications if you hunt for them.
Also if you take two photos one exposed for the shadows and one for the highlights its possible to blend the two photos.
here is a blending article
http://www.luminous-landscape.com/tu...blending.shtml