I was once involved with this sort of thing
Our product was evaluated by Forrester and Gartner. Forrester had a detailed list of questions, they went through on screenshare timing how long it took to perform certain standard tasks for that type of product, and how many clicks, etc. They'd get us to do it again if they weren't happy.
Gartner just said, "we can evaluate your product based on your company's overall position in the market." This was a company with 20--30 different products.
Couldn't believe the difference. Not happy that they're a source of news for El Reg.