We use our ePro for our non-merch purchasing, basically anything we don't sell to our customers. We use the IaaS (Infrastructure as a Service) model. This has served us fairly well. Support is good but at times it is not as responsive as we'd like. Not having to manage the hardware or OS is nice but also limits how to manage or troubleshoot issues.
As for the system itself, it is very configurable and meets most of our needs. That being said if you are in the process of implementing ePro make sure you know very well, or have a resource that is highly knowledgeable with best practices in designing your workflow. If this is not done correctly, you can end up making a lot of extra work with changes that inherently come with a system over time. We use this as a standalone system with very minimal integration and it works albeit not as efficiently as if it were more integrated with our financials.
Overall I like the system especially the ability to have a vendor portal for real time notification/communication on POs. ( a function we have not utilized as of yet ).