Hi borisav,
It’s amazing how much a cancellation can bring the prices down 
The worst part is that you know they are still making a good profit even with the extra discount.
I would not consider it or any other “S” brand as a good option and they are all poor value. A post I made (post #22 here) just before yours has more about the “value” of mainstream brands and the frustration of trying to find out any meaningful information about what is in them only to discover if you do (and this is not so easy) that they are not comparable to many better choices that are made by local or independent privately owned manufacturers.
At least Watertown carries a couple of independent brands that may have better quality and/or value (Gold Bond and Symbol).
In the case of the Beautyrest classic firm plush … you can see an example here that it has at least 3" of a mix of low density polyfoam in the upper layers which is exactly the type of foam I would try to avoid. If you want to pay even more and have even more lower density foam that has an even higher risk of softening prematurely then you can buy something like this. These types of mattress can be purchased with the same or higher quality foam at lower prices made by local independent manufacturers all across the country. Mattresses are only as good as the materials that are inside them.
The industry is not the same as it was 10 years ago and mattresses specs have been lowered in every price range. All the mainstream mattresses are not bad quality as you mention (although they do their best to make sure that the quality can’t be determined at all) … they are just poor value. Even their best are significantly overpriced compared to local manufacturing sold factory direct or through better sleep shops. This video is well worth watching … and tells the truth about what has happened in the industry.
Phoenix