I am in the market for an EOTech: 510 or 550.

Whats the difference besides the battery and lengh?

And why should I go with either one.

Ant info will help

511 and 551 use "N" size batteries.
512 and 552 use "AA" size batteries.  

You get much longer run time with AA batteries.  

The 55x models are Night Vision compatible and cost about $50 more than the standard of each battery type.  

I used to see the 511 for $300, the 551 for $350 as well as the 512 for $350 and 552 was $400.  I think prices have fluctuated a lot since I 'memorized' that little 'formula' for remembering the differences.  

Me two I like the Eotch 1moa

but dont like the longer AA

longer run time but for me its to big.

I think Im might get the N battery now wich one NV or regular?

I went the 512 for two reasons.  I didn't mind the extra length and I liked the fact that I can AA batteries anywhere.  Also, the life of the AA's is longer than the N and AA lithiums are even longer than alkalines.  Also, I had no need for the nightvision model so I decided not to pay for the NV feature?

There's a dealer on these boards that sells the 511 for less than $300 from what I've heard.  He doesn't advertise the price in his ads but supposedly an IM will get you one for somewhere around $280 IIRC.

If you can get your hands on a few sets of spares of "N" which is no problem then go ahead and get the non NVG 511.  It's the same as the others- only difference being the batteries/battery compartment.  

If you want a real cheap version, get the bushnell holosight.

You can still use NVG on the lowest setting but it's supposedly not safe and may 'burn' a reticle on your NVG.  

Maybe a burnt-in reticle on your NVG wouldn't be a bad idea.  You could then just sell the Eothingy...

I had an older 552, but I didn't need the NV compatibility, and felt it was too big.
Just replaced it with a 511.
I'll keep some batteries in my TangoDown Battlegrip, and it shouldn't be a problem.

just traded three 511s for three 512s. I could not stand the battery life of the N battery. AA last MUCH LONGER!!!!

Slug-O

You could pick a model that suits what you will be using it for.

I just got a model 551 (NV, N battery & short model) because I wanted to have a smaller package for use with a NV which I plan to get later on.

The battery life of this model is not great but it's adequate enough for my intended use.

If you want longer battery life get the 512, 552 or even the new, coming soon model 553 which is also a long model.