The advantage of the OEM windshield kit, provided it comes with the lock, is that it really is extremely easy to remove and reseat the windshield, and the kit doesn't look ugly at all. Actually, you don't even notice it, just a few bobbin type fasteners, while the Memphis one leaves a lot of iron behind on the fork assembly when you remove the shield.
The lock in principle is the same lock as the one used for the bags and sissybar, which are just as easily removable if you have the locks installed, so one key fits all.
I had the Memphis kit on the XVS1300, and the OEM kit I have on my current ride, the XV1900. I prefer the kit on the latter. The Memphis one isn't bad at all, but the OEM version handsomely beats it, if you'd ask me.
Personally, I'd save up a little, and go OEM in this case - with the lock option
Kind regards, Wim