So let me tell you why our dear Kylo Ren’s lightsaber is terribly designed…
AHEM
Cross guards are meant to protect the users hands from another person’s blade…
The crossguard was developed in the European sword around the 10th century for the protection of the wielder’s hand
Little Kylo Ren’s lightsaber is as a big of a danger to himself as anybody else because of those vents placed into the hilt of the saber (the red things meant to look like a cross guard). It’s not like Kylo Ren is magically immune to his own lightsaber while everybody else’s can still hurt him. Even though it is clearly supposed to look like a cross guard, it clearly wont have the benefits of being a cross guard.
Those vents are there by the way because Kylo Ren uses a damaged crystal for his lightsaber.
Which brings us to the next point.
Using a cracked crystal for your lightsaber can easily prove unreliable… the crystal could become even more damaged from wear and tear and you can suddenly find yourself without a working lightsaber. That’s a pretty dang unacceptable risk when your only physical weapon is that lightsaber. Just you watch, in Star Wars VIII I bet Kylo Ren’s lightsaber crystal is destroyed in some kind of lightsaber fight with Rey… leaving him weaponless.
I mean how stupid can you get. “Yes I am going to use a damaged saber with these hyper dangerous vents oh and the blade is all ragged and imprecise too because the crystal is too powerful but that’s okay who needs precision this is such a great idea”.
To Sum Up
Kylo Ren’s lightsaber design is terrible.
And ultimately Kylo Rens lightsaber is designed purely from an aesthetic point of view and/or as we may discover in later Star Wars films ,as the story develops, from an emotional point of view.