We have recently install or added a vMX100 to our AWS VPC. It was straightforward as long as you remember to use the token within 1 hour :-) "Read the documentation if you don't know better" :-).
There are some limitation on what you can do but it was not a showstopper in our case.
I have only hear rumours regarding Meraki will start supporting BGP features . That will be great since that will mean we can get a fully HA setup towards AWS instead of this single point of failure. So good look.