You can do Trackfone for around $5 a month.
You purchase time and pay the 5 a month and you do not need to add time until your time runs out.
Jitterbug does not require you to purchase time in any way. If you never uses it you are never charged. You just "rent" the opportunity to use it for $10 per month.
If you do decide to use it then it is a pricey 35 cents per minute. So for me that is just $120 per year. No minutes to roll over or run out or worry about. I seriously never use the cell unless it would be an emergency (911 is free).
Also, my jitterbug number is an 866 toll free number which makes it easier on someone who needs to contact me if I am 3000 miles from home..
But, the reason I like it is the phone. Nothing like it that I have ever seen. It feels like a real phone (showing my age).