There are no immigration controls between Ireland (ROI) and the UK... which means your visa won't be stamped to show what date you entered the UK (it's actually illegal for them to stamp your visa if you are coming from Ireland due to the rules of travel within the Common Travel Area (CTA)).
This can cause problems later down the line with other visas/immigration if you need to prove what date you entered the UK on your visa... because there will be no immigration record showing when you arrived and you will need to find another way to show that you were physically in the UK on that date.
So, because of this we usually advise not to enter the UK through the ROI for the first time on a visa, if at all possible.
You are fine to travel to the UK via any other country... it's just coming in from Ireland that can cause the problems.