Ease of purchasing and set up. Love pliable yet firm feel of mattress: it's what we were looking for. Our only remaining adjustment is to the edges of the bed as you sit on the mattress; there's more 'give' and we are getting used to it, but feel it's just a matter of time.
It's affordable. Great quality, vouched by other household members who've taken naps on it. Backed by a long term warranty, so there is a feeling of security if any signs of sinking in the bed show up.