There have been several different devices with the generic "Jetpack" label from Verizon. So you should use the actual model number to be specific.
My 4620L has worked perfectly for over a year on both 3G and 4G in many different areas, and I'm very happy with it. But I have read many online reports where others have had issues with the 4620 going dormant and not reconnecting on demand. Not sure if those are hardware issues, user issues or tower issues, since mine never experienced any similar issues.
My one caution, depending on your previous 4G use, be prepared for your monthly data usage to increase significantly. The 5 gig monthly Verizon limit used to be way more than enough to cover my frequent internet use for the years I was limited to 3G. Now that I frequently get 4G coverage, my monthly data volume has actually approached the 20 gig limit of my Millenicom plan. I don't feel like my usage has changed that much, but the numbers say it has.