Hi blewis,
From quality/durability point of view … all the layers use good quality materials so this is the good news 
I can’t comment on the “deal” you are getting because I don’t know the price you are paying or the importance you place on any of the other factors that are part of the value of any mattress purchase (see the list in post #46 here) and how each person decides on their personal “value equation” but at least the part or this that includes the quality of the materials is good and there are no obvious “weak links” in terms of material quality.
Price and “commodity” value is only one part of the value of a mattress purchase though because no matter how good the “deal” … if a mattress doesn’t fit your needs and preferences when you sleep on it and if there is no recourse (or your recourse is too costly) if you make a mistake with an online purchase … then no matter what the price you paid for a mattress … it would have little or no value to you. Don’t forget that quality of materials has little to do with how suitable a mattress may be for you because even the best quality or value mattress may be completely unsuitable for any particular person in terms of PPP (pressure relief, Posture and alignment, and Personal preferences) and with an online purchase you are completely dependent on the knowledge and experience of the person selling the mattress and of course on their exchange or return policies.
Hope this helps.
Phoenix