You can't really blame them for the second point, that's an Apple limitation.
I use OpsGenie on Android and I have a specific sound set for the new alert notification. It will also audibly alert me at max volume regardless of my ringer volume or DND setting.
I do agree about the multiple source numbers of SMS alerts but they're hardly the only person who does this.
Can't say I have had many issues with their UI. It's fairly straightforward. The only annoyance for me is ack'ing or closing a number of alerts at once and getting a bit of lag.
Also, iOS doesn't allow you to set a custom per-app alert sound, so I can't set one there that will wake me up when stuff is broken.
Also the UI on their app is marginal at best - multiple taps, no back tracking, etc.