Not understanding why anyone would advise against this or where you got that information.
Ultimately, it doesn't matter what anyone else thinks. It is yours, if you want a koshirae made, go for it.
Cost is the only reason I can think of why anyone would advise against having having a koshirae made.
Depending on the style and the level of quality, your budget may be insufficient. It is not cheap to do.
Keep in mind that there are additional costs incurred outside the koshirae itself. Shipping, insurance both ways, torokusho fee, broker fees, etc., etc.
Also, it is time consuming if you plan to have it done traditionally whether here or in Japan. Curing Urushi takes quite a while.
There is a process for importing a blade into Japan. I wouldn't call it complicated, but it is subject to the Japanese rules and takes a little time.
I am preparing a couple for shipment now, have one currently awaiting the next Shinsa.