Nope, VM don't cap your bandwidth, and usually they offer the full contracted speed (in fact, usually a bit more, so my 200 Mbps connection runs at around 218 Mbps). Reliability is, in my experience, a little bit less that Openreach, but not sufficient to make much difference. Where VM really differs is latency ("ping" for the uneducated), which tends to be very slightly worse than Openreach if you have a good connection. Ordinarily this won't be a problem. Where VM do have a problem is in areas with high user numbers where this leads to congestion and really poor latency (particularly due to lockdown).
But why not give VM a go? Get a connection, keep any existing broadband uncancelled, and see how VM performs in the first ten days of your "cooling off" period. If VM is good, you cancel the previous ISP, if there's ANY problem you cancel VM, and pay nothing. But do read other customer's reviews on sites like Trustpilot and ISPReview before committing.
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