I've been reading through hundreds of posts in this forum silently, which can reduce some stress coming out while waiting. I just wanted to add my timeline here so as to add a datapoint

Visa Type: Tier 4 General to Tier 2 General, Super Priority, no dependents
Date of Online Application: 18 Jan 14PM
Date of Biometrics: 28 Jan 9AM at London Croydon – around 10AM after biometric taken + passport pages scanned. I think the UKVCAS service was good.
Date of Email Decision: 06 Feb 12PM
(Gosh! 7 Working Days after biometrics! This came right after my MP's email reply and my 1st-class "large letter" arrival at UKVI, The Capital Building, New Hall Place, Liverpool, L3 9PP)
Date of Decision Letter: 08 Feb 10AM (showing decision made on 06 Feb)
Date of BRP Delivery: 22 Feb 3PM with my 1st NINO number (my ID wasn't checked by DX...)
On 12 Feb I asked the status of my BRP to 'BRPDelivery@homeoffice.gsi.gov.uk', surprisingly they replied me on 15 Feb that there was a delay on BRP production because they were waiting for the Department of Works & Pensions to confirm National Insurance number (quite an interesting ‘newly aligned’ system ha…). I also wrote a complaint to 'complaints@homeoffice.gov.uk' for the delay of visa decision, but no replies or refund received yet. I may write a letter and post to the complaints team in early March.
I think that both contacting local MP and posting something to "UKVI in Liverpool" might work better than calling or emailing to UKVI. Good luck to everyone!