Been a month since I switched to Unlimited Zen Fibre 2 from the ADSL2+ Package and not had any problems. Speeds normally about 70Mbps.
My only quibble is the line rental. Went from Home Talk Plus to Line Rental Plus and increased by about £5+VAT, no mention of this when I ordered over the phone, so it feels like I got no line rental discount for having both LR and BB through Zen. I did query this with an email to billing, a month ago, but as of yet not had a reply.
So what I though was a £5 upgrade from Zen Active to Unlimited Fibre turned out to be a £10 upgrade because the line rental increased as well.