[GoneBallisticInAlabama]

Being a completely new line of pistols with a lot of buzz since their announcement, and likely huge backorders, Sig is using all their parts to fill orders for complete pistols and try to get the remaining variations out as quickly as possible. Since the fire control unit is common to all variants, those parts will probably take longer to become available for purchase anywhere than getting out say a conversion kit for a variants that have already shipped and filled initial orders.

But I think that the FCU is probably quite dependable and shouldn't give any problems.

I think you will be fine to go ahead and get one. The time until they are available will pass quickly.