This is not a better deal than you can get on other machines. I would not buy one of these machines without first having tried out Janome or Kenmore machines with similar features and price. Here is a link, for example, to a Janome Jem Gold that many people here have and like:
http://www.sewvacdirect.com/janome66...a_7cjano_d_660
It has been years since I sewed on a Necchi, but I remember them as being loud compared to other machines. Rightly or wrongly, I have always associated loudness with poor quality; my Bernina purrs!
With one-day sales pressure like this, you can be sure that the $529 price has been inflated. The 25-yr warranty isn't anything different than other sewing machines have; same with the features offered. As for the serging attachment, very few people ever use this. The stitch is not the same as a serger makes, the machine does not run fast like a serger does, and the cutting mechanism on the attachment is clunky compared to a serger. This is an attachment that can be purchased separately from the machine anyway.