The Millenicom plan is excellent if you think you will actually take advantage of the full 20GB/month but could be a waste of money if you do not. If you already a Verizon customer (AT&T has a similar plan) you can take advantage of their Share Everything plan. You pay for each smartphone getting unlimited minutes and text and then you decide how much data you need. You can add a MiFi device to the account and you simply connect your computers and surf. I only average about 6GB/month and we full time with 2 phones, 2 computers and a Kindle Fire.
We do supplement our cellular usage with campground WiFi when "good" service is available but that's usually less than half the places we visit. It I do need more data I can just go online and raise my data allowance which only adds $10 for an additional 2GB.