UDP is treated fairly well by firewalls... at least compared to SCTP for example. QUIC/HTTP3 are UDP-based and even though there's usually a TCP/HTTP2 fallback they fare reasonably well.
I have various boxes which we send out to venues, on the whole outgoing connections are fine, but sometimes you get some really restrictive policies. I've had stuff that MITMs TCP/443, completely blocks UDP, etc.
My devices tend to try to connect back via
* UDP port 443, sometimes works
* an sstp vpn
* SSH to tcp/$highnumber, sometimes they blck/MITM port 80, 443, but leave the standard
* DNS
I can't think of a time that one of them didn't through.
It does make it through many firewalls these days, yes.
But all implementations I know use a much shorter timeout/keepalive period for UDP than they use for TCP because of firewalls/NATs. (I think the RFCs even recommend something like 300 seconds for TCP, but only 30 for UDP as a default?)
This has pretty significant implications on power consumption for mobile devices.
