I had a perp mount on my M4 while I was in Iraq, and had a reflex site on top. I had no issues at all with sighting it at 100yrds, I sighted it the same day I sighted in my 3-9 scope. Anytime I engaged targets under 100yrds or if I was clearing houses and buildings I used it with great results. Another plus is also , once you do get it sighted in you don't have to have the dot in the middle of the sight glass, as long as you can see the dot no matter the angle you'll be on target so don't worry with check weld. Thats why they are called reflex sights ,for quicker target acquisition allowing you to shoot with both eyes open.
Not trying to hi-jack either , just throwing in some of my experience with the topic . I have also taken targets at 300 meters on military ranges with the reflex alone. (Nice rifle sendit)
Sorry Hogstir , yeah you'll be just fine at 25yrds.