I am well aware of sizes and weights.

"Toxic effects begin to occur at doses above 10–20 mg/kg of elemental iron. Ingestions of more than 50 mg/kg of elemental iron are associated with severe toxicity"

^^^^ that is for humans so unless reptiles process iron differently (which they very well may) a 250 gm BP could exhibit toxic effects at a lowly 2.5-5mg, (think dragging a damp rat across exposed rust.)
Until I see info regarding reptiles metabolizing iron safely I will prefer to err on the side of caution even if it costs me a little bit more.