These do exist - they're used in the NHS to measure how well therapy might be working, and they're part of the reason that CBT is so popular these days. I think they use the Core Outcome Measure. I have one of those forms with me right now actually, if you're interested. They use them at the charity I work for.

They don't ask specific questions about the therapist, that would be an interesting and worthy addition. They just aim to measure the client's general "wellbeing".

Obviously, for the reasons SD mentioned above and many more besides, they're not a perfectly reliable measurement at all. I've had to fill them in and I found them to be slightly ridiculous - it's very difficult to reduce all your thoughts and feelings down to a tick in a box. But they're an attempt to measure how well therapy might work - and I guess no-one's thought of a better way yet - if a better way is even possible.