You don't
need a cellular Apple Watch to take advantage of fall detection. You just have to have your phone within range of your watch and the two need to be connected via bluetooth.
If Apple Watch detects a hard fall, it can help connect you to the emergency services if needed.
support.apple.com
Not saying a cellular option isn't beneficial in some aspects. A BOGO deal is something good to take advantage of if the deal strikes your fancy.
I traded in a Series 4 WiFi on a S6 coupled with the discount my carrier was offering when buying a new iPhone it was too hard for me to pass up--so I understand the temptation.
![Stick Out Tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Performance wise, I don't see a significant difference. Sure Blood Oxygen, Altimeter, Compass and AOD are nice features to take advantage of. No regrets.