I first started using APM when it was Wily. It was a game changer at that stage and hasn’t looked back. CA have continued to build and improve how it works and how it integrates with other products. APM should be utilised at all stages of an application lifecycle. It provides detailed insight of what is happening within the application, be it SQL response times to how many webcontainer threads are in use. Issues that arise are easily highlighted by APM and should be reviewed by the necessary support team within your company.
The product is expensive in both monetary and footprint terms. In my opinion, a standard configuration requires 4 servers to run APM. So between licensing and hardware, the product is not cheap. Once you have the hardware provisioned, I found the installation process relatively easy but the documentation is not as clear as I would have expected. I ran into several small issues but they were resolved. I found it difficult to find the right person within CA support to answer my questions. They do have forums and user groups which should make life easier. Upgrades can be time consuming if you have many agents. You need access to the servers, resources to do the upgrade, downtime from the application owner etc.
If you have an unlimited budget and so can afford the CA suite you will have a very good monitoring solution. If you are managing a budget, I’m sure there are cheaper alternatives out there.