It can be used without a cover, but it definitely needs protection when traveling and the most common damage to E-Ink screens is from strong local pressure (e.g. from an object pressed against the screen) which a cover protects against.
I have the M-Edge Kindle cover, and I'm not sure the "suede" interior is leather (I have the same cover for my iLiad with the same interior, and ereaderoutfitters advertise it as having a "soft cloth" interior). I suggest checking with
M-Edge. The M-Edge cover is an improvement on the original, and I recommend it.