Hi scubamom,
You may need to replace it much sooner than you anticipate or believe you will … without warranty coverage (as you can see here … warranties don’t cover the loss of comfort and support that goes with lower quality foams softening more quickly). These types of mattresses are also much more costly than the materials inside them would justify.
This may not make a lot of difference if the lower quality materials in the upper layers of your mattress are too thick (which is quite likely) because the latex will just compress into the layers underneath.
The Black line is among the worst of all. You can see some examples of the materials they use here and you can look at any of the models and you will find that every one of them has significant weak links in terms of the quality/density of the comfort layer materials they use (even the firmest ones).
I would avoid them completely and treat them as “buyer beware”.
Phoenix