My opinion, but yes they are equvalent in crack or inclusion finding.
Having worked in and around a large machine shop all of my career I have seen both used. We also used x-ray and ultra sonic testing.
Die Pen was used on non ferrous, non magnetic materials.
Mag particle on alloy steel, cast iron, etc.
x-ray on open root welds
UT on bar stock to find cracks and voids that would surface during machining.
If you have die pen ability make sure the heads a squeaky clean because residual oil will mask problems.