Hi Jason - the process to access trials can vary, but generally you would need to reach out to your reseller and have them connect with their Broadcom team to request a trial on your behalf.
Regarding comparisons, cloud and on-prem EDR features sets are at near-parity. On-prem does require an EDR appliance (virtual or physical appliance) and therefore requires an architecture cost. Cloud Endpoint Security and EDR requires no infrastructure - the endpoint only needs to be enrolled into cloud and an EDR policy applied.
If you have any specific questions, happy to try and answer those here.
Also, Symantec's YouTube channel is still quite active. Recommend you browse through there where you can find several short demos/overviews of both EDR as well as the cloud (Endpoint Security) manager:
https://www.youtube.com/user/symantec/videos