I think MJ is refering to the fact that if you use a RDS your eye will be seeing 2 dots (one from your rds, and one from this front site) competing for dominance when setting up your sight picture. This could be viewed as counterproductive and may slow you down.
Assumption is the mother of all ****ups.
Know what you know, Know what you don't know. -Paul Pedzolt
"Jack of all trades, master of none, though oftentimes better than master of one" -Mynshul