I would think it will not roam onto AT&T being that tower is miles away and the Dish tower is less than a mile away. I had an AT&T hotspot before and I had to use an antenna for it. Will this antenna work at all with the Dish hotspot? I don't know what bands I may be getting. Below is the link for it. Being it is still on the mast I could check it to see what it does.
I tried that type of antenna as well as one that suction cups to a window with the Netgear M1. They worked OK, but this one worked much better. Again this is with the M1 model. I believe there is a 5G version of this antenna.
I have used that antenna in the past, but it was not working for me at my current location. I got this antenna from Amazon and it works great.
My internet is an AT&T Nighthawk hotspot. I have an antenna connected to the hotspot antenna port and it improved my signal/speed considerably. I have trees also and this is on the mast of my OTA TV antenna.
Get one of the nortel jetpacks with external antenna port then one of these
Wilson Electronics 700-2700 MHz Wide Band Directional Antenna with F Female Connector - Retail Packaging - White https://www.amazon.com/dp/B00KY4Q7AY/ref=cm_sw_r_other_apa_RP4Txb2925RRY
I used to work on drilling rigs in middle of nowhere USA and would hook that up pointed to the closest tower and would get 2 to 3 bars of lte while the rest of them couldn't even call their spouses. Just pay attention to what you need for connectors and don't cheap out on cabling or get longer than you need. Most signal degradation is due to people cheaping out on the cable.
Edit: I understand your concern with the mifi, but for what is worth about 500gb is still being used on it and so far no problems. I'm a risk taker though.
Wilson makes great products. I have 2 of these. They work great Wilson Electronics Wideband... https://www.amazon.com/dp/B00KY4Q7AY?ref=ppx_pop_mob_ap_share
I have this antenna connected to my Netgear M1.
I have this connected to my Nighthawk AT&T hotspot and it works great. But it is on an antenna mast outside.
You might want to head over to https://www.reddit.com/r/CellBoosters/new , might be better for antenna and booster questions.
Most cell phones don't have an antenna port to connect to, so an antenna wouldn't work. Jetpacks or LTE routers often do. If you want to help a cell phone, a booster would work.
I have a booster. This is the antenna (ohm rating needed to match the booster). If you have a jetpack, you'd need cable and an appropriate adapter. https://www.amazon.com/Electronics-Wideband-Directional-700-2700-314475/dp/B00KY4Q7AY/ref=sr_1_3?crid=2TNO0NXRXSMM4
It works 11 miles through a lot of trees, and 13 miles no trees, here.