I've had three covers on my Libra Colour. All sleep covers. I'll share my thoughts on them.
First I bought it with the official cover. I bought mine on release, so it was the only one available. It was quite lightweight, but I am not a fan or the origami style covers, preferring a book style. It also didn't properly cover the sides and edges of my libra, so I didn't think it offered a great deal of protection. Like every other kobo official case I've owned, it wore at the edges after less than a year of ownership, so off I went to aliexpress for a new one.
I got
https://a.aliexpress.com/_EuNrcgm this one. I liked the design and I wanted one with the crease at the edge, as I find opening the cover easier with it. It covered my Libra nicely, better than the official case. I was quite happy with it. However, I knocked my Libra 2 off the arm of the setee I was lounging on and it fell to the carpet from a height off less than a metre. It must have hit the base if the chair at the right angle, because a corner of the case pinged off, leaving a big chunk out of the plastic shell of the cover. It did its job, protected my Kobo, but I would have expected it to stand up better than it did.
So now I have
https://a.aliexpress.com/_Exy51GS
It's a cover like the one I have on my phone, like a transparent silicone type shell to safely cradle my Libra 2 in see through plastic, with raised edges and corners to protect it. It shows off the white of my Libra 2 nicely and I know some people like to put stickers and things on the kobo back so they show through the cover. It also has a lightweight flap to cover the screen that seems to hold securely. It is the thinnest and most lightweight cover I've had, but some people might not want the feeling of a phone like case on their e reader. The flap folds back fine for reading and the sleep wake function works. I confess I've only been using it a couple of weeks though, so I can't speak for robustness and longevity.
I don't think it adds much bulk or weight, so I would recommend it.