First off the quality is GREAT.
I purchased the download in addition to the Hard cover book. I would have purchased both no matter which came out first. It does have a couple typos, a couple charts were wrong, but overall it is a great game and I really enjoy it. They have already released a FAQ, covering the typos, fixing the charts and explaining a few areas.
I think the rule set is very easy to follow. Some people complain that it is not detailed enough, but I don't nor do my opponents have a problem with it.
I am a diehard fan of Dust both Tactics and Warfare therefore, my opinion is based as such. It is well worth the twenty dollars. I really like that with the same miniatures I can play two different but similiar games depending on my mood and my opponents.
I look forward to the additional releases and will purchase both hardcover and a download copy.
I really don't think you can go wrong with the download copy. This is the first time I have ever purchased anything from the Wargame Vault and if the quality is always this good then I know I will be making additional purchases.
Hope this is helpful.