I don't think LambdaTest has any scalability issues, as far as I have heard from my team.

It is a scalable solution. We are three end users, and we are planning to extend the usage. 

Twenty five users are using at the moment. The scalability is an eight out of ten. 

Good.

The scalability is good with Amazon, but IBM had some issues.

As said, we perform multiple tests for browser coverage, so we have scaled up our testing pipeline and are now running multiple tests in parallel. This scaling up was way too easy. No more adding VMs for testing locally.