We use mifi along with a EnGenius WiFi signal extender. The reason we purchased the mifi, was to give us access at CG's and surrounding areas that had no public WiFi. The mifi cost us about $90 for 3Gig, which we used up in no time at all. We just returned from out trip to Colorado (4 months) and only needed the mifi at 2 CG's, out of the 14 we stayed at, which did not provide any WiFi. We tested the signal strength of the extended WiFi vs the laptop's WiFi only, and the results were as expected (Really Great). It also allows you to select the CG's fastest AP (if more than one is available) , which the laptop alone did not see. I use it to connect to the Slingbox connected to my home cable, VPN, and the signal reception was great, watching the home DVR/cable (Ray's Baseball). The MagicJack phone works great with it.
As for security, if you have a good firewall and antivirus program on your laptop/PC/Tablet (I only use McAfee, as did all the companies I worked for), set them up for public access, and ensure that the sites links are https access, for your private information, you will be ok. I mostly use the VPN connection (encrypted data) that links my TT directly to my home internet connection, and search the net that way.
Good luck with your decision.
I can only speak for myself, it is not for everyone, but we are very happy with our system.
Our WiFi Album - http://www.jaycoowners.com/album.php?albumid=328
2013 Jayco Eagle 284BHS
250Watt Grape Solar Panel, MorningStar MPPT 60 Charge Controller
1500 Watt Ramsond PSI, 2 Trojan T145 Batteries (260Ah)
2 - AirSight Wireless IP Cameras (used as rear view cameras)
EnGenius WI-FI extender, D-Link wireless (n) modem
MagicJack Internet Phone
2012 Ford F150XLT, EcoBoost w/3.73
157" Wheel base, HD Towing Package
Our Solar Album http://www.jaycoowners.com/album.php?albumid=329