ISPs monitor and modify your internet traffic in America (perhaps that's different in the UK?). My American ISP absolutely spies on me. So rather than accept that guarantee, I can use a VPN like Mullvad who at least promise not to do this, and whose entire business relies on keeping that promise.
> whose entire business relies on keeping that promise.
That "you should not use a VPN" link someone posted elsewhere explicitly disproves that claim, saying that HideMyAss were caught breaking their privacy promises and have yet to go out of business.
The prices of VPN services also don't make sense and potentially suggest something nefarious is going on (not saying Mullvad is doing this, but any VPN advertised on YouTube is very likely to do so). It's difficult to imagine that they can afford such bandwidth/hardware and the amount of support/abuse cases (remember that VPN services will attract scum as a side-effect of their privacy/anonymity claims) for such a low price.