We use REST API Transaction for 2-3 steps transactions.
They took usually up to 5 seconds.
The highest frequency for this type of monitors is 10 minutes.
Having very tight SLA'a it is to less.
We need to have 1 and 5 minutes frequency.
In addition this type of monitoring should have a simple shell access to be able to run basic & simple scripts (otherwise it is difficult to use this feature comparing to jMeeter and Zabbibx).