Well even the sp3 is still not a laptop and you have to purchase the extra keyboard for $150 I believe. Its basically a windows 8 tablet which I'm not so crazy about. Probably wont get the same battery life as the galaxy tab s, and wont play my avia player for my chromecast. I may hold on to the tab S after all, its pretty good for the type of pdf reading I do.
This is true, probably just as expensive as the extra MS keyboard you would need for the SP3.
You could use any keyboard with it. A $10 usb keyboard, a $50 bluetooth keyboard, or the keyboard cover. The Keyboard cover is not your only choice. That said, a laptop (or surface) and an android tablet are not really the same sort of device and I am not sure why it has to be a one or the other thing unless you don't REALLY have a need for a laptop. Because if a tablet is being considered as a viable alternative then it has to be said that you don't really need a device like the SP3.
You could also use any keyboard with your Samsung tablet. A usb keyboard or a bluetooth keyboard. Just no PS/2 keyboard.
Personally, I have both the 10.5 Tab S (returned my 8.4 today) and a SP3. I only take out the SP3 when I really need to.