FWIW, all Arista hardware is AWESOME. They run a lightly modified very minimal linux operating systems that is very clearly (not even really hidden) Fedora. I got the privilege / opportunity to reverse engineer one of these to see if it was hackable (ie: add custom hardware into them or run apps directly on the switches).
Pretty much the entirety of the Arista userspace is python with all of the magic really in their ASICS. Truly, I've not seen many better engineered pieces of equipment. At the time (I did this > 4 years ago), the Arista switches had dual core AMD Athlons with a few G of ram. They were willing to put more RAM in one, or let us upgrade it. For a so called "vendor product" Arista clearly gets it. They have some really solid Linux guys working for them. When you get the pleasure of using their python apis or pull one apart, it shows that they know what they're doing. It isn't completely insane to think of running apps directly on the switches when they are simply x86_64 Fedora boxes with some fancy asics and a lot of interfaces.
1) low individual component cost (which is great when you need 100's of them for a datacenter build out)
2) no frills, high throughput non-blocking backplane which are normally only available from the enterprise grade network vendors at top dollar per individual component, and come with a mountain of features and bugs you DONT NEED
3) software defined networking stack: if you can imagine a scenario/feature that would improve your life, nothing but development costs will get in your way. contrast with enterprise vendors, which requires explaining the problem to begin with, and dangling a wad of money explaining how it will be worth their while to develop it
Almost all "open" projects seem to hit a point where the line between open and closed is quite arbitrary, even if they choose not to see it that way.