If Signal becomes financially dependent on government contracts, the govt gains a lot of leverage over the app. I'm not sure that's a great position for this particular platform to be in.
Certainly it's better for the gov't to pay Signal than to try to do it themselves.
The MobileCoin integration and the long standing refusal to support a way to use the messenger without using a phone number (or a smartphone at all) make me wary. To me they sit pretty much on the same level of trust as Meta's WhatsApp, which is a sad thing to have to conclude.