The Eotech has a metal hood that goes around the glass. It sticks out all around the glass casing and acts as armor to protect it.
From what I've read, they are the same internally. The name and protective hood are the only differences. It's a tough choice. The other option is to buy an Eotech 512 or a version without night vision capability. It might not be as "tactical" but they are significantly less expensive. Just another option.
The one thing I do like about the Eotech, are the 553 models with the quick release. I use it on my AR-15 upper and my .22 AR upper. Holds zero and comes off really quickly. I find this helpful when changing between a scope (Also with quick release rings) and the Eotech. The AR system is really versatile. This just helps you get the most out of it.
By the way, shooting metal with an AR .22 upper and the Eotech, is a heck of a lot of fun. This combination is perfect. The only issue is, missing becomes so rare that it's almost boring. The speed and accuracy at close ranges sure is amazing. Lots of fun.