It is scalable. We have not yet had a problem with scalability.  

I am impressed with the scalability on our side. Our management is not investing in scaling up the service. It's quite stable at times but sometimes they give us headaches also. We have issues with the BPM lock not expanding in time. It becomes slow because it needs to expel the DB log. 

They are very scalable because I can go from one to a dozen of them.

The solution is scalable, but then, even when you scale it, the performance is an issue.
There may be scenarios where you may not be able to reach the optimal performance that you're looking for.