I don't think my wife would be happy with that, but I'm just trying to establish the reality of what it is they offer.
It has blackouts of local teams so you could not use it to watch O's/Nats unless you want to involve a VPN. It also does not show nationally televised games, so you cannot cancel ESPN and then watch that.
But other than that, yes, HD feeds of every game (with the option to watch either teams feed) and you can get the app for your phone to watch there too (or listen to the local radio feeds) for no additional $. And many Smart TVs/Tivo/video game thingies have the Mlb.tv app so you might not even need to buy a Roku depending on what you have in your home already.
For people like Smackie and myself who live out of market for our favorite team, it's glorious.