It depends . . .

Is there any possibility of an out-of-phase condition developing between the incomers? Many of the industries I dealt with that were connected to feeders 44 kV and below took it on faith that they would never be supplied out of phase and therefore had no synch check facility of any kind, and to the best of my knowledge after 44+ years we as a utility never broke their faith.

In areas where there is grid-connected generation with dual grid-supplied M-T-M facilities the situation is different; there I'd without a doubt go with "c".

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

In installations where the customer has a M-T-M we likely feed the two mains from different substations, but who are normally in phase. That said, it is possible for them to be out of phase, but that has not happened.
The customer installed sync-check.
This is better as that customer now wants to install generation, which will require it.

Even when feeders from two substations are "in phase" it does not take much voltage or phase angle difference to create large circulating currents should the tie connect the mains together while both substations are connected. Syncro check might not be the only permissive for close you need.