I've never used cellular boosters, but I have spoken with several RV campers who swear by them - they tend to say that if there is no signal, there just is no signal - but if there is just a bar or two, then the cellular booster will make a significant improvement for voice and data transmission - more for voice than data. A larger external antenna can make a significant improvement in an area with a marginal, but present, signal. Generally a higher antenna is better than a lower one, and the top of an RV is better than a hand held device in a low sports car or motorcycle.
Don't expect them to let you watch Netflix in the outback however.
And I would point out that some cellular services have much better cellular coverage out west than others - there are counties out west - where a county may be 50 or more miles in diameter, where there is only one cellular carrier even present.
If you go to your carrier's website, they should have a map of their coverage across the country.
I know that some National Parks cellular coverage is effectively non-existant, but it varies greatly depending on where the park is and what its size is. There were certainly areas in Yellowstone last winter without any service, but sometimes when we got higher in a pass, we could grab our email out of the sky. Some National Parks, more in the east, tend to have better coverage.
One other distinction needs to be mentioned - some of the cellular boosters are for fixed base/ non mobile situations - rural homes needing better cellular service, like the Cel Fi in your post above. They also tend to be cellular carrier specific - that is they are specifically set up for a specific carrier.
The We Boost is a mobile unit - the truckers tend to have cellular boosters in their cabs these days so their websites might be a place for a recommendation as well.
I would also mention that the Overlanders who really get off the beaten path tend to drift over to 2 meter FM for more reliable communication in the field. But for that you need a radio license.