I'm with Joe the Wincer on this-- when a vendor claims they have an integration, it means nothing to me at all.
First, you have decide *why* do you need the integration. Mostly the vendor's requirement is to claim they have an integration so people will buy their product. Lots of naive people will buy only on that basis, and not validate that what the vendor's product does is what they need done in their organization.
I lean towards a best-in-breed preference so long as tools in question have an API I can use to access any functionality I need. Then I know minimally that I have the building blocks I need for whatever solution a given client has requirements for.
Somebody has already mentioned the cost of maintaining that custom "glue", which I acknowledge is a factor. But then, so is the cost of buying a tool that turns out not to meet your needs. Or the cost of discovering that you thought you bought an end-to-end solution only to discover that now there is a new technology you want to use that doesn't fit in your chosen solution. Or the cost of discovering that your IT assets depend on your chosen vendor's good graces, because you can't swap it out for an alternative.
To mitigate the cost of glue, an organization could subject the glueworks to the same code review and testing rigors they use for their other IT IP.