1) No because we don't use PPTP VPN. We use OpenVPN which is not subject to the flaw mentioned above hence why we have stuck with OpenVPN despite IDevices supporting PPTP.
Quote from the article:
One alternative to PPTP is OpenVPN and offers a number of advantages, especially as it's free and open-source. It's more secure than PPTP, and more stable too, though it doesn't work on mobile devices natively and isn't quite as easy to set up on a computer, especially older machines. OpenVPN also has the advantage that it's often not blocked in countries where PPTP systems are blocked.
2) If you're not using it (it's a different address system), then you don't need it. Generally it should be ok on. Disabling it shouldn't affect speed though sometimes faulty config/drivers/programs can get confused by IPv6. This is rare though and shouldn't be the case.
3) Yes it will be an issue with other PPTP VPNs.
