Have you done a free trial? I would start there. The most basic Umbrella package, Professional has the roaming client which adds security and works off net. Insights adds historical data for incident investigation.
So, to answer your question directly, I would say the roaming client, the additional visibility to security threats and maybe some scare tactics around recent news of ransomware, etc. should help you get buy in from the boss.
- Ex community all-star (⌐⊙_⊙)