Caps are there to show how much usage you are getting for the monthly charge, it is usually something i avoid, but if you are not a heavy user then it may be okay for you, as they will either charge you for the overflow (If you go above the cap on amount of data down/uploaded in the month) or they may deny you access, the latter isn't that common though as far as i know.

What is the speed of the connection offered, as that would be easier to translate into data sent and received over the month??

Liam