Their rollout is pretty major and without trying to sound like I'm plugging them (I have no reason to), then eventually this will be Yuge.
As a whole Zen are still growing on the business side and last year they took on loads of new staff. Not just 'any' staff either, a lot came from other ISP's or industries, so even the CS type aren't noobs and less likely to be script monkies.
They have put millions into investing new equipment. I think (hope) what is going on right now is teething problems as they switch over to the new system.
If anyone can come in from behind and do this right, then it should be Zen, because when it is completed it will make them a major player in the UK up amongst the big boy names.
I think they have shown foresight. PN realised that the BTw MSILs weren't working for them and gone dedicated to give them more control. Zen have taken another approach and are quietly plugging away in the background to build something big that they can call their own. The fact that they mostly support business products means that they cannot afford to muck up. I really do hope this works out for them, when completed it will give them a prescence throughout most of the UK. How many other SP's have attempted trying to take BT as much out of the picture as they can - although obviously they will still be reliant on Openreach.
The weird thing is they are quietly coming in from the rear and getting there. There are some other well known names in the industry who have faith they can do this and are watching and waiting. Because their target audience is business rather than consumer, then the media seem to have little interest.
You can read more about it here.
https://www.zen.co.uk/latest-news.aspx?page=12218