Hi James,
Your requirements can be fully managed with our standard modules. It will be great if you can share the country your company is based on to see if Tryton has the localization chart by default or you will need to create your country localization or setup your accounting manually.
This should be an important point to take the decision.
Sincerely I do not know enough details of ERPNext to give this comparison. I know they use a similar stack (Python and PostgreSQL as backend) but IIRC they only have a web interface, while on Tryton we have a desktop application and a web interface also.
I will try to summarise some good aspects of Tryton:
- We prioritize quality over quantity: we may have less features but we focus on implement them very well and complete
- One result of the previous point is that Tryton is so much stable and we have stable and LTS releases
- There is a very active community on this forum which may help you if there is some issues but there is also a list of service providers if you want some professional services
Probably there are more things of the list, just wanted to share some, maybe some other members may complete my reply 
Feel free to ask if you want to have more detailed information of some points that are relevant for you!