We have a number of SRG 50s (really just BCM 50 hardware with a different license key) providing a number of small business offices E-911 PSTN access and local survivability should the WAN to the Call Server 1000 fail.
I just noticed today that you can't manage a SRG 3.0 (older release) with the new version of BCM Element Manager (v61.0.0) that comes with the SRG 5.0.
That's really annoying...