There’s some adequate info on eotech 553sights on this site A lot of the 553 models are hard to find much out about but I’ve been considering buying one. The site has lists retailers to buy as well as some reviews.
The name of the website is Tacoptics.com and it’s actually laid out pretty well. There are a good few links to find EOTech 553 brand optics on Ebay which looks to be it’s primary purpose. It’s put together well enough that it’s acutally somewhat simpler to find particual sights than just searching ebay and it doesn’t come across as spammy. The reviews are useful but look to be more just a statement of features than personally thought out. Most of the auction deals are somewhat less than most other places and I wound up getting an EOTech 553 for a pretty good deal.