Garmin buyers typically choose the brand due to the much longer battery life, however Garmin doesn't have any magic battery technology - the longer battery life is simply from less full time services. If enabling the additional hardware functions that bring it on-par with the ultra, the ultra actually has a longer battery life.
The other issue is that both brands diverge in how they offer satellite connectivity. For iPhones, satellite connectivity includes messaging, sending locations, and carrier-provided functionality via satellite (e.g. SMS), alongside with the road-side assistance and SOS features. These are included at no cost (at this time).
Garmin on the other hand starts with a $40 activation fee, then a minimum per month charge of $8 USD which then still charges 50c per text message, $1 for voice messages and 60c an hour for location tracking. Garmin's also offers a $50 USD per month plan where some of these tariffs are included, but notably voice messages are limited to 50 units before reverting back to $1 each. The $40 activation fee prevents users from saving money by switching off the functionality when not needed.