yeah, one free action knife/round per persisted echoing invisible spell cloud of knives is the whole trick...
but if we start by casting one, 24 hours later we have 1 +1+1... up to twenty four, so one spell slot got us twenty four echoing persistent invisible spell cloud of knives. and this shenanigans carries on day after day, but with adding more spell slots for compounded knifey interest.
but Ihadn't ever thought about doing the trick with persisted telekenisis... good call, but not sure if it is feasable pre-epic
cloud of knives is 2nd lvl, +6 from persistent, +3 from echoing, which counts as 9th thanks to incantatrix (or as 6th with arcane thesis and invisible spell).
telekenisis is 5th, so i guess that works in a 9th slot.
either way, both tricks work in the end i guess... or would, if MotUH could have both 5 lvls in the prestige class and ninth level spells. although, we can probably add other +0 metamagics to have the telekenisis work.