Hi KrazyPanda,
The latex you are looking at from Sleep On Latex is a blended continuous pour Dunlop (Puralux) which is generally a blend of 20% natural and 80% synthetic rubber. It is among the lowest cost versions of latex.
I would consider the blended Talalay from either Latex International or Radium (which both use a blend of about 30% natural rubber and 70% synthetic rubber in their formulation) to be very durable materials and closely equivalent to each other in terms of durability. There is more about the different types and blends of latex in post #6 here but all the latex you are likely to encounter (Dunlop or Talalay made with natural or synthetic rubber or a blend of both) will be a durable material relative to other types of foam and the choice between them is always a personal preference and/or budget choice.
I would also consider any exchange or return policy as being part of the “value” of a topper purchase.
All latex will use a formula that includes foaming agents, curing agents, accelerators, gelling agents, antidegradants, and sometimes fillers … but synthetic rubber is just as much “rubber” as natural rubber and isn’t a “binder” (although “too much” filler can reduce the useful life of foamed latex). Any version of latex would be a good quality material and wouldn’t be a “weak link” in a mattress.
Phoenix