Provided you have a decent wireless signal then you should not notice any slowdown in teh ADSL link speed. Even a basic 802.11b will give 11Mb.
As for using providing access to others - how close is any other property or road? Will anyone realistically use it? If you believe it will be NO, then stay subscribed as you will get free access when you are away from home. You can always opt out later on.
One other point: m - milli or one thousandth, M- Mega or one million Your speed will be 0.75 to 2 Mb (Mega bits). Similarly b- bits, B- bytes.
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