Add-elle sounds like 'addle' to me, as in addled eggs. Yuck. EEV-lyn seeems to be a fairly common pronunciation here, but I think Ever-lyn is much nicer.
The various non-Welsh weird pronunciations of
Megan drive me nuts, but I think the silliest I've come across was a student I had called
Vivienne, pronounced Viv-EEN.