Here's my dos centavos. I'm sure there will be 10 guys jump in with exactly the opposite experience but here is mine.
I bought a 66i about a year (maybe 2 now..) ago. It's a rocket ship. It can do everything. But, it's also a hot mess. Garmin bought InReach - and I think some other companies and cludged everything together.
You can do a lot of neat stuff with it on your phone - after you figure out the clunky system. You need to have 2 apps running on the phone or laptop (connect and explore) in order to make it sync. THen you can do some stuff only on the explore app - some only on the connect app- and some only on the unit. Also, don't bother trying to connect with the cord. 3/4 of the USB cords don't work - even Garmin sent me several in hopes that at least one would work. Fortunately, you can do all the updates etc wirelessly - even though I didn't think that was very clearly explained.
You really want to use the phone (or ipad) app with it. It is so much easier to scoll and zoom through maps on your phone than on the unit.
I have used Garmin a lot because I had units on boats for years from way back in the 90's. If I didn't have that experience I would find using the unit extremely frustrating - and even with my experience I sometimes get a bit exasperated with the damn thing.
I do really like the web portal that they have for your laptop. It's kind of cool. But, again - it's not intuitive and they have a bunch of outdated software (basecamp for example) that they no longer support, still make available, but don't do a good job of explaining or migrating you to the newer software.
I carry it for the SOS button. I spent a few days off grid with my 10 year old. He always knows where the unit is - and how to use it. When we put on our waders or grab a pack - I tell him where it is on my person (along with my keys, cell phone, and anything else relevant BTW) and make sure he knows how to use it. We even sometimes run through the scenarios (for example - 'if I couldn't talk or fell down what do you think the right action would be?').
It's nice to be able to send texts but I find that I use that feature A LOT LESS than I thought I would. Even off grid for a couple of days I think I sent 3. All anyone needs is a quick 'I'm safe'. We can catch up on stuff when we get back in cell range.
But that's me. YMMV.
I set up my truck so the 66i has a mount/charger on the dash. Then I sync it with a small ipad that is also mounted on the dash. My son and I spent several days driving around exploring and we found we preferred using Gaia about 90% of the time. THe only time the Garmin was better was if we hadn't pre downloaded a map for a certain area. In that case, the Garmin was far superior because we already had the maps in it. BTW I have BRMB on both the garmin and Gaia. BRMB definitely worth the money.
I wish Garmin would buy Gaia and just move to the Gaia system for mapping. Then I think we would have the best of both worlds.
If you're in Vancouver or can catch me when I'm up at my cabin near Kamloops I'm happy to let you play with the unit and software.