We don't set a limit on how many users can use an extension at the same time.
Use Case Example
Can 1000 people fill out a form in a minute and nothing breaks?
If 5 of those 1000 people save the form at the same exact second, then the Airtable API limit will be reached. If the 1000 people would submit the form over the span of 3-5 minutes, then there is no risk of reaching the limit, but there is a risk of reaching the limit if 1000 people all submit the form within the same exact minute. We have not seen our users hit the Airtable limit with our form, but we suggest spanning those people over a few minutes, rather than concentrating them in a single minute.
Airtable API limit
The Airtable API rate limit is 5 requests/second. In the rare case, if you hit the Airtable API limit (e.g. when you have many edits at the same moment), some users may get an error -from Airtable- and they'll be able to try again. If the API rate limit is reached, there's a short timeout period set by Airtable before the ability to make API requests is re-enabled.
miniExtensions automatically retry to submit if the API limit is reached. If the request fails after retiring many times, the user gets an error. Users only see a loading indicator on the screen while the system keeps retrying in the background until they see a success message (or in extremely rare cases, an error).
In case you receive extremely high submissions at the same time and you hit the Airtable API limit, the form will still load. Some users may get an error when they click submit, but they will be able to wait a few moments and click submit again. The data in their form won't be lost and they won't have to restart.
Our customers use miniExtensions in a production setting every day. We've only seen the API limit becoming an issue when you have thousands of users updating your data at the same time. So if you don't expect that to be the case, then you have nothing to worry about.