The defender is like getting a fat kr808 manual batt with 750mah rather than 380mah which is I believe what the XL batteries now provide....so it lasts longer. It also has a cone to put on top of the cartomizer but I am not sure what that does except make it look better than without it, but can be used without it. Recharge the batt when it runs out of power and replace batt when needed....just like Kr808s. Not sure what voltage..prob 3.7 mostly. It has 808 threads.
The SP is an aluminum tube housing that you put a mod battery inside and then screw the carto on top. You take the battery out and recharge the battery when it runs out of power....kind of like a flashlight. Button is on the bottom.... SP is about the size of a tube of lipstick without carto screwed on. Only replace 16340 3.7v batt that you buy for around 6$ when needed. Batt with it has 880mah. Very durable and all mechanical, lightweight metal with no sensors or electronics to break....plan to use mine working in the yard and fishing.... ie.where I don't want to take my Chuck. It has 801 threads but comes with an adapter to use 808s with and works fine. Can stand on end and sturdy...button will not go off.
Wisteelerfan has a review of the SP on vapewithpuff.com (puff's blog)....you can find it if you put spark plug in the search feature on the blog....it has pics too.