I have not used these Black Friday deals before 
Will it go lower on Friday ? or is it day by day deals ? and are they just 'on-line' ?
If its listed as a Black Friday event, then no it wont go lower on Friday. The PCWorld/Currys offers are usually in store, via phone, or online. Samsung Direct is online only.
Be warned, a lot of the the deals go very fast. Last year I was online just after midnight and a lot of the Samsung Direct deals had already gone by 12.30.
I bought via Curry's/PC World Black Tag Event. Last year the offer started at 1 minute past midnight and iirc lasted over the weekend.
Unfortunately the one I ordered got damaged in the post and when I rang up immediately on the Sat morning, it was
1) a nightmare trying to get through because there were so many people trying to get hold of the offers by phone as the stores were out of stock.
2) They didn't have any more of the one I originally ordered (bronze/gold) in stock in any of their stores or online. But luckily they did still have a black one which they sent instead.
Ive ordered quite a lot of online things from Curry's/PCWorld, delivery is normally very fast and this is the only time I have had a damaged package from them. You could tell from the packaging before I even opened it that it must have been dropped on transit. :/ (Actually it looked like it may have been stood on! and I said as such to the driver).
They use DPD which is usually very good and have a decent online tracking service so you literally know to the minute when its going to be delivered.