We are in the same situation. I used to use Alertra but things pretty much stay reliable and a lot of customers comment on that, so I dropped it.

We were asked about uptime in a pre sales question the other day and managed to track down some numbers from findmyhosting.com who measure with Alertra. We havent been asked about stats like that for a while... but our main source of clients is referrals and with that happening people just dont ask and accept if their friend likes the account then they will have one too