micro swivel or bait screw make the rig so much easier to tie, but i dont think either way effect the effectiveness of the rig...with the exception of weight!
And with a pop-up, maybe a swivel could be the way to add some weight to hold the pop-up down, but that is worth a thread in itself (Pop-ups and how they behave under water may be worth looking at )
As for the bait screw, I have always worried about piercing the skin of a pop-up, so I have tied mine on for many years
Nick , the avid bait screws were initially designed for use with the avid hi-lites , the fake boilies which take on flavours whilst guaranteeing never to take on water and therefore never sink . I have done some tests and they keep ordinary cork dust and airball pop ups perfectly popped up for more than a week in a tank test (and 48 hrs in the lake , i've never fished longer
I know you are one for testing stuff so just thought i'd mention it , its made my fishing so much easier what with arthritic fat fingers etc