Redis Pub/Sub vs Rabbit MQ

RabbitMQ is far more stable and robust than Redis for passing messages.

RabbitMQ is able to hold and store a message if there is no consumer for it (e.g. your listener crashed , etc).

RabbitMQ has different methods for communication: Pub/Sub , Queue. That you can use for load balancing , etc

Redis is convenient for simple cases. If you can afford losing a message and you don't need queues then I think Redis is also a good option. If you however can not afford losing a message then Redis is not a good option.

Redis is a fast in-memory key-value store with optional persistence. The pub/sub feature of Redis is a marginal case for Redis as a product.

RabbitMQ is the message broker that does nothing else. It is optimized for reliable delivery of messages, both in command style (send to an endpoint exchange/queue) and publish-subscribe. RabbitMQ also includes the management plugin that delivers a helpful API to monitor the broker status, check the queues and so on.

Dealing with Redis pub/sub on a low level of Redis client can be a very painful experience. You could use a library like ServiceStack that has a higher level abstraction to make it more manageable.

However, MassTransit adds a lot of value compared to raw messaging over RMQ. As soon as you start doing stuff for real, no matter what transport you decide to use, you will hit typical issues that are associated with messaging like handling replies, scheduling, long-running processes, re-delivery, dead-letter queues, and poison queues. MassTransit does it all for you. Neither Redis or RMQ client would deliver any of those. If your team wants to spend time dealing with those concerns in their own code - that's more like reinventing the wheel. Using the argument of "not willing to learn a new product" in this context sounds a bit weird, since, instead of delivering value for the product, developers want to spend their time dealing with infrastructure concerns.