All I can say is Superb! We have been using them for 2+ years and prior to Tranxact Global|GNAX, we have used various DCs and ended up with GNAX. I think the premiums paid compared to other DCs are well worth the service. We have used Nocster, Ev1, SM, and local DCs before moving to GNAX.
It will be much better if you could check the support request response time. You can do this by sending some pre-sales request emails. This will determine the response time that they are providing to their clients as well as the potential clients.
Their support tickets time may vary. If you submit a ticket and call them 2 minutes later, it's two minutes. If you wait, it may take up to 5+ minutes. Their sales emails lack, but if you call and speak to a sales rep/billing rep, you will be taken care of on the spot.