With each subscription you get a production branch and up to 20 staging branches.

While a production branch [shared tenancy] can scale up to support 200 back-end concurrent users [dedicated tenancy is available to support higher numbers of concurrent users], each staging branch can only support 25 concurrent. 

These are not hard limits, but average. It may be possible for a staging branch to support 30 users, it might be too slow with 20. Each branch has a Monitoring tab that presents common performance statitics such as memory usage, cpu usage, storage, number of requests, number of concurrent requests and average response time. You can use this information to help you better understand how similar or different your usage is to the average.

If you need to onboard potential users and wish to use staging branches, you can support up to 500 average users if you spin up the full 25 we allow.

If via monitoring you determine you need more resources, you can purchase another subscription - an "onboarding subscription".

We can link the code repositories of the two subscriptions, so that as a development is made available to your production subscription, the same development is pushed to your onboarding subscription. It is also possible to download a backup of your production database and restore it to a branch in your onboarding subscription, in a similar way that creating a staging branch duplicates your production database for testing purposes.

This is an example of response times for a staging branch, you can see users are waiting up to 7 seconds for some requests:

This is an example of response times for a production branch, you can see all users are waiting less than a second for all requests:

If you need your onboarding system to reflect the PERFORMANCE of your production system, the second subscription may be your best option. 

If you only need your onboarding system to reflect the FUNCTIONALITY of your production system, the 25 staging branches may be your best option.

Additional Resources:

https://www.odoo.sh/faq

https://www.odoo.com/forum/help-1/how-many-workers-do-i-need-with-odoo-sh-145771

https://www.odoo.com/documentation/15.0/administration/odoo_sh/getting_started/settings.html#database-workers

https://www.odoo.sh/pricing