I tried it and it worked well until the boiling wort deteriorated the cube and the beer tasted of burnt plastic. I don't think it's worth the risk.
I very much suspect you didn't have a robust HDPE container. I have run over 50 brews through my cube and the only thing it smells like is hops... I have never actully even heard (before) of anyone having a cube "become" rubbery/plasticy, but some people, including myself, get plastic taint from new cubes. Always soak them in boiling water and taste the cooled water.. When i cant pick it in a triangle test from boiled water cooled in glass - then i'll use it on my beer.
If your cube was made from something else, or perhaps you just got a bad one... But this experience is so far from normal that it might well be unique.
Not an off the wall or alternative method here in australia - hundreds of brewers and multiple award winners using this technique, as well a quite a number of commercial ventures selling craft brewery wort that is hot packed in exactly the same way.