"...had assumed it would use the shard as I felt it was the only possibility that made sense to me." - Really? So the rental costing essence as a possibility never occurred to you?
To me, someone that made the mistake clearly doesn't look at details. There's no way I would have fallen for this as I would be wondering how much essence or whatever I would have to spend to rent it. The fact that the cost is the shard itself definitely makes me think it's not a rental. I'm no English master, but I had the same initial thought that this thing wouldn't cost itself if it were called a rental and I'm sure many people have had it.
The movies we watch don't tell us, "This movie will self-destruct in 5 seconds if you are not the true owner of the media it is written on." at the end of the show.
I guess the reason people are upset with it especially is the same reason I would be if I were in their position. You can't get a shard back after you've rented it. If you decided you really wanted it afterwards, you're basically screwed and have to buy it the old fashioned way, with RP. You missed your chance to get it through the loot system and are unlikely to get that chance again.
Now if they are upset because they can't get essence from it or to use it as another one of three for random stuff, then I can get on the bandwagon and ridicule them for their silly greed. You don't rent stuff for free. That's called borrowing. As it is, the most I can do is belittle them for not bothering to do the proper research, like going on YouTube and looking at skin previews.