Id like to be very accurate out to 300...not necessarily just a longer range.
That will be up to you.
A reflex sight will be no more "accurate" than iron sights, usually less so.
Red dots are faster, easier to use and better in low light than iron sights, but they won't make you "accurate".
What size target are you wanting to be able to hit at 300 yards?
Can you resolve the target that you want to shoot at that range with an un aided eye?
Remember, a red dot is just the reflection of a light on an angled lense of glass. Don't get your expections set too high.
The only thing that I have experience with is Aimpoint and Primary Arms. There is no comparison between them, the Aimpoint is leaps and bounds ahead of the Primary Arms in performance and durability. But the Primary Arms is good for the price.
It is a great way to try out a Red Dot without spending a lot of money. It will let you try it out and if you like it, eventually when you buy a good quality Aimpoint, you can move the PA sight to the M&P 15-22 that you will invariably buy as a .22 LR training/practice rifle.
(When you do, I can give you pointers on how to get a lower 1/3 cowitness to match a Larue optical height.