the advantages of the UL frame also are the compability of the other UL board and triggers, though you have to buy new eyes in some cases if you buy an after market UL board. As stated the UL frame is heavier and you lose the ability to use the after market parts such as the trigger guard and power buttons. I think that for £20 it is something you may as well get, but if you wanted a NDZ or trinity frame it would mean a new board, grips and trigger. So it depends whether you are going to upgrade, as the stock frame PMR after market triggers such as the VP sycthe are very nice. Though there are compatible triggers for UL frame, some are not available in the same style as the standard PMR triggers