Just to update everyone,
I'm happy to report that the experience of ordering from RS is good.
1) very fast response to emails, same day response (if working day/ office hours)
2) delivery is as stated in order page: in my case (in stock for delivery within 4 working days), I ordered on Tuesday and received the item on Friday. My item shipped from UK warehouse some more.
3) the delivery company used is GDex.
4) pricing wise, some items are cheaper than others (eg. element14, Mouser, Digikey etc.) but some are more expensive. Some items require MOQ of 5 or more compared to other sites which offer MOQ 1 only.
5) best of all, free delivery for all online orders regardless of how much you order.
That sums up my experience in ordering from RS Online.
And thanks to all who helped answer my questions here.