I know, to pay this price for a sub cover seems excessive, but trust me it is essential.
I tried to resist and my very first gig with the Sub618 is got a scratch. Just bite the bullet and buy the cover to keep your gear looking great.
Quality wise, this is a tight fit and very basic - the covers for the Opera 12's for example have a lot more give and are more functional wise zips so that they can stay on the speaker while in use.
This cover is as basic as it gets, and has to be taken off to use the sub which is a pain. But as a basic cover to prevent your sub getting scratches, it does the job.
A lot of room for improvement (like using the sub with the cover left on) but it does the job for preventing marks while being transported.