Hi MrM1 and 203sbvert,
I’m not sure where you read that this wasn’t acceptable but it would certainly be a suitable choice for a mattress in this budget range or even higher (see the guidelines here). There is also more about polyfoam support cores in this article. You may have been reading the article about comfort layers which suggests avoiding 1.5 lb polyfoam comfort layers in a one sided construction because the weakest link of a mattress is generally in the upper layers.
While this is somewhat of an old subject because the change was made a long time ago … it has been the subject of many questions (probably because of an Amazon review that talks about it shows up on top of the “negative” list) and you can see my thoughts about it (and the review) in post #2 here and the posts it links to (including the post that MrM1 linked).
For most people that aren’t in a heavier weight range 1.5 lb polyfoam would be fine and this would be a very good quality/value and durable choice.
Phoenix