If you are getting cable it wont disconnect unless there is a fault VM's end.
In comparison to ADSL it rock solid stable with no fluctuations sync speed.
Throughput however can be a lottery, some areas are oversubscribed, some aren't. Although on the 30-100Mb tiers it's less of a problem than on the older tiers.
Good news:
"The legal stuff
Money back guarantee: The 28-day money back guarantee is available for new cable customers and existing cable customers taking a new service. Call us within 28 days of service activation to cancel and we'll refund the first month's charge and any installation charge. You will only be charged for transactions (calls, texts, purchases, service upgrades) occurring after activation. Statutory rights not affected."