I got up to 21 E1’s of traffic in one single voicemaster, I cannot say that has been ZERO problems, but most of them have been really reasonable fast solved and the equipment is running very stable.
We do not have to forget that the Voicemaster acting as a gatekeeper does not handles the payload but the signaling of SIP and H323 calls.
If you have any question about training or purchase let me know I am in Miami, Florida.