I've got the Tacstar +10 extension on my 870. Been pleased with it so far. Put it on shortly after I bought the 870 a year ago.
so it's 10 rds total? because on tacstar website its says minimum 26"(i have a 28" barrel) for +10 and on nordics website their +9 adds 23" after the barrel lug. so im assuming the nordic actually adds 9 rounds and the tacstar adds to the existing rnd count.