I think you need to decide what you are looking to do.
SIM can send you emails on hardware events without Insight Remote Support. IRS is for use with systems that have a valid HP contract. I would not use it just to monitor/send emails. The products are separate, but can work together, but neither is required for the other anymore.
Both products are "free" for what you want to do, there's just no reason to use IRS for monitoring/emails only, unless you want HP to automatically open cases for your contracted hardware.