This far out I would go very far to avoid the mentioned OTA as schedule changes or cancellations are likely. As you already know this is when the troubles start... For immediate travel I have less concerns.

I don't think you need to worry that the ticket will not be honored or the airline will make you pay more; the issue is that OTA will refuse to co-operate when needed, is difficult to get in contact with, or will mess things up by e.g. not reissuing ticket after sch. changes and rebooking etc.

MyTrip and GotoGate are affiliates, i.e. the same - and from my experience amoung the worst. Lastminute I don't know.