Portable Hotspot or Portable Wifi Antenna?

I have been thinking of getting a personal portable hotspot, such as one offered by FreedomPop or YourKarma, where there is a monthly allowance of free cellular data. As an alternative, I would be open to some sort of portable wifi antenna that would allow me to use a weak wifi signal to a wifi network I can normally connect to when the signal isn't weak. I have a $100 Amazon gift card to use for the purchase. I don't want to have anything that requires a credit card even as a "backup" after free data is used up.

I have been considering purchasing a portable hotspot, such as one from FreedomPop due to the free monthly data available, but have read many horrible reviews. I currently can't find YourKarma available on Amazon.

I currently have to go outside in front of the school I volunteer at to connect to an Xfiniti wifi network, as I am not allowed to connect to the school's secure network with any of my personal devices (iPad, and laptop). Inside the school, I can often detect the Xfiniti wifi, but am not able to actually connect to the Internet with it because the signal is too weak. I want to be able to get online to check or send email and have at least basic web access without having to go outside every time.

What is my best option? Please state your sources (even if it is just from personal experience). In case it matters, I am in the SF Bay Area, California. Thanks for your time.

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