Really depends. Of course Heroku is way more convenient, but you can squeeze quite a few small apps on a $10 VPS. I'm not sure how they count ressource usage, but maybe an even smaller tier would be another option.
That said, for testing and stuff for personal use only the 18h deal is fine (although technically trolls could just go around calling random heroku instances every half hour, burning through the awake-time on free instances). And I can understand that they want to limit free usage.
And of course Redhat OpenShift still gives you three apps for free ;)