We have recently started using EchoSpan's 360 tool for some of our leaders. Currently using a "pull" methodology in which leaders or departments use if they are interested. Purpose is to get our people feedback on what they're doing well and what they need to work on.
I've seen or used several of the other 360 tools. EchoSpan is better in nearly every way. It is more customizable. It can be administered completely by someone internally, so no need to request someone to set up a 360 - you can just do it yourself. Competency library is great, and you can create others if you want to. Reports are easy to interpret. Very good customer service.
I can't imagine a scenario where it is less appropriate than any other 360 tool. It's easy to use, customizable, and inexpensive. Reports are easy to interpret. Great tool for anyone looking to implement a new 360.