Not any more. The factory .357 Sig Sigma barrels were solid, but the aftermarkets had some problems. I would be leery of any leftover aftermarket Sigma barrels.

The cheapest way to get the switch-barrel setup is to buy the M&P, which has factory barrels availble in .40 and .357. They drop right in , with no fuss.

9mm conversions to either .40 or .357 will always have the challenge that the 9mm case head is just enough different from the other 2 to somewhat mismatch at the extractor.
Not impossible, but not always reliable either. A fellow shooter spent the price of a gun trying to make one conversion work, and it never did.
One poster on this forum took a 9mm Sigma barrel, chamber reamed it to .357, then carefully fitted to his .40 slide and extractor: about 6 hours careful work. He reported it functioned correctly. Neat bit of precision gunsmithing, but expensive if you have to pay for it.