Enterprise product E will cost your team X hours of time to develop expertise.

O requires install time. E either requires install time or integration time.

When O breaks, it is likely that the community has already seen this problem and can provide suggestions via docs, mailing list archives, discussion fora, blogs... Your team's expertise will increase. If your problem is interesting, the developers will likely get involved.

When E breaks, you will open a ticket. Within 24 hours, someone from the E company will try to diagnose your problem, going down a flowchart that they will not share with you. If your problem is in the FAQ or flowchart, it will get solved within a week, probably. If your problem is interesting, it may eventually be solved in a future release. Your team will spend less time working on it, but E will be broken for longer.

You will pay dollars to your team to support O, which will make them happier.

You will pay dollars to the E company to support E, which will make them happier.