What I have heard is that their support and documentation is quite good, but I don't have personal experience here.
A few things to consider:
Kentico only uses SQL Server ... so if your clients have policies for example to only use Oracle databases, this might be a problem
Further: It does not have the possibility to create static HTML sites. And if I am right (not sure here) this does mean that the webserver will need access to the database (because not everything works via remoting), which means that you might have a problem with some company policies.
One other option is perhaps to check out axCMS.NET ...