We use Zen internet, 10mb/10mb on a 100mb carrier, no problems what so every. Takes around 3 months to get installed.
We have a total of 3 Fibre connections to fora resilient connection to our head office including a MPLS line, these are not supplied by Zen but done globally by the company.
The ADSL offering on the business park was so slow it was unusable for what we wanted to do. So we had to go for a leased line as there were no other options such as Ethernet First Mile (EFM).
In the end all three lines were installed by openreach engineers just paying different people along the way.
J