The three key reasons to go Aviatrix Transit over any other native cloud transit solution are:

1. Multi-cloud Architecture

2. Operational Visibility 

3. Advanced Networking and Security Features 

1. Multi-cloud Architecture

No native network solution delivers multi-cloud networking with a common data plane across multiple clouds. Even if you are in a single cloud today, you want an architecture that you don’t have to redesign when you go multi-cloud.

2. Operational Visibility 

No native transit network solution provides data required to deliver enterprise class operational visibility. Dynamic topology mapping, detailed network traffic flows, geo-location traffic flow heat maps, remote packet capture, remote traceroute and remote ping.  Intelligent analysis of route tables and security domains to verify correct configurations and help troubleshoot connectivity issues to the source/destination, port and protocol level. All built into the Aviatrix transit network.

3. Advanced Networking and Security Features

No native transit solution provides enterprise class features such as Active-Active high availability with full reliability by running paired gateways in separate availability zones, end-to-end IPSec encryption, high-performance encryption (up to 75 GBPs) and support for next generation firewall insertion that maximizes throughput performance and maintains source address visibility by eliminating the need for SNAT.

One more way of describing it.

 Here's a table from our Transit Capabilities white paper that has been very useful for a lot of decision makers. DIY efforts drain valuable resources away from the organizations core competencies, while missing out on Aviatrix capabilities and features that are supported by a vendor and continuously improved.