I have used both and i only will buy a FFP scope ,here is why , I target shoot and hunt , I am always changing my scope magnifications , say you have a 5x20 scope here is some reasons why I only use FFP ,
so as you can see a FFP is always true , if you hunting , and see a squirrel and are at say 8x with a SFP and decide to hold over , it can be confusing you may thing you on a different magnification and you dont have time to put to 10x to make it true mil ,by then the squirrel will throwing nuts at you ;I doubt he will stay put if you say wait I got to get out my calculator and figure out my hold
EXAMPLE
ok we sighted in at 50 yards with our 5x20 scope and we shooting 100 yards we calculated and it is a 4 mil hold
FFP scope
5x 4 mil hold @ 100yards
10x 4 mil hold @ 100 yards
25x 4 mil hold@100 yards
SFP scope (true mil magnifaction is at 10x)
5x ?????????
10x 4 mils
20x????????????
However , f you a target shooter and say shoot same range all the time then it is ok to use a sfp , I however dont just shoot paper at identical distances
LOU