The double-saber is fine if you weild it one-handed. The main problem with Maul is that he tries to use it like a staff, which is isn't. It'd be excellent if used in a similar manner to a Madu (an indian double-bladed buckler/sword combo weilded in one hand). It could also use considerable improvement, because it definitely needs a proper handguard. Unfortunately I'm not finding a decent video on silambam techniques with maduvu, or I'd post it for reference :/ ; generally, though, the doublesaber design works when used one-handed and makes for a solid defensive weapon that you can weild offensively rather nicely as well. When you start using two hands you sacrifice all your mobility and stuff gets a tad nonsensical.
Dito on Ren's sword design. With proper use and grip, it's virtually impossible to cut yourself on the crossguard. The offensive capacities of said crossguard are rather nasty as well, much more so than the defensive ones (where the design is noticably lacking). There's a nice video with a somewhat exagerated crossguard design that illustrates how here:
You'll notice that neither Ren nor Maul actually use the weapons 100% realistically, but that's movie fighting for you. It doesn't necessarily mean the design themselves don't work. They just need to be handled properly and with care.
Edit:
I guess I can toss in two wiki pages at least that give the general gist on the first paragraph:
https://en.wikipedia.org/wiki/Maduvu
https://en.wikipedia.org/wiki/Silambam
Edited by DeathByGrotz