It is really cute, but it is going to get nasty pretty quickly and its going to be hard if not impossible to clean. All of the little holes in the perler beads and the gaps between them are going to fill up with algae and bacteria. Also I would worry about his fins snagging or getting scratched on any rough edges.
I had that same idea when I saw it. It will be a pain in the butt to keep bleached and cleaned. Didn't think about the rough edges, though, but you are right. Good point. It is cute, but maybe better if sealed in some form of acrylic, so that it was more like a plexiglass feature. With solid walls between the openings.
I find it funny that people are so worried about the effect that this is going to have on my tank. It's not my first fish rodeo, guys. In response to the above concerns...bleach should never, ever be used on anything that is going to be put in a fish tank. Soap isn't even tank safe. Also, algae growth is easily controlled with proper lighting, tank water parameters, and weekly partial water changes/gravel vacuuming, all of which are implemented in my tank. As far as the bacterial concern, you actually want the beneficial bacteria to grow in your tank, because it's a sign of a healthy system. The bacteria colonizes and starts the nitrogen cycle which converts ammonia to less toxic nitrates. So, no worries there. And lastly, have you seen the decor they sell in stores? The pretty fake reefs and and caves? Run your fingers across those bad boys next time you visit a pet store. Ouch.
So no worries. Kevin is completely safe and happy in his perler bead condo. All aspects of this project were researched before I made it.