Hi llazos,
You can read more about their materials and design in posts #2 and #6 here and as you can see there are no lower quality materials or weak links in their design that would compromise the durability or useful life of their mattress or result in a mattress that was sagging prematurely.
In other words … you made a good quality/value choice … and congratulations on your new mattress 
I’m looking forward to finding out how you like it once you’ve received it and have had the chance to sleep on it for a bit.
Phoenix