People have had trouble with fiberglass monofins when they've never swam in a monofin before.... But the foil or wave/rapid aren't so pricey and people have less problems learning in them.

Something to keep in mind I think, because that way you don't lose $300USD on a monofin when you could save that money to go towards the actual tail. A foil only runs about $50USD and the wave/rapid only a bit more than that if I recall.

That's what I would suggest, because it's a much smaller chunk out of the tail fund, and you're also not left hoping your tail maker will agree to put an old used monofin in a brand new tail, and you're not stuck paying shipping and handling fees if they do agree to it.