Ok, so obviously a lot of lightsabers are homemade when they're not passed on as ancient artefacts down the Jedi generations, but the close up reveal of Kylo's saber seems to confirm that it's not actually very well made. The splinter used to create a crossguard effect might be an ingenious addition (it might also not be, since nobody can actually fathom what logical reason there would ever be for adding it), but the way the energy crackles angrily seems to suggest that it's barely contained. And even better that it's somehow an abomination of true Force nature (perhaps because Ren has effectively stolen his powers or manipulated them grotesquely). That's probably the perfect allegory for how we should consider Rene: bursting with energy and teetering on the edge of control. Let's just hope he's not going to be killed off before the end of the first movie, robbing him of a chance of becoming more powerful than we could possibly imagine...