I never tested it but my Guess would be that you are better Off with MIFI since it is a dedicated tool for this Job. A Tablet that engages at the same time in other activities and run other processes might not perform as well as a LTE MIFI.
However, if the need involves only simple text activities (email and light surfing) it probably would not make any difference.
If LTE dongles for Laptop are already available, I would get one for the Laptop, then use the laptop's native Wireless to act as a Hot spot for the Tablet using this free software.
http://virtualrouter.codeplex.com/