I've been using Onspeed for a couple of years with GPRS/3G. It saves a factor of several times on the cost (PAYG data is normally charged per byte).
The system sets up a www / pop proxy which your machine connects to instead, so it's transparent.
However, two problems
1. The Onspeed resident program does a fair bit of comms with their server to set up the connection; around 10-15k bytes and that can slow things down if you just want a quick connection
2. The Onspeed servers have slowed down hugely over the past year. I think they are playing the old ISP game and milking their assets for all they can. Max profits are always made just before total service collapse
Back to the subject, I find wifi works over a fairly short range unless one is using a directional aerial. In this case that's what I would get. If the signal has to pass through two outside walls there won't be much left otherwise.
And yes, security.... the neighbour will see everything on your PC, unless you enable the login/password login option and then it's best to not have any shares, and disable the Guest account.