I've been using the free Chronoforms 3 for a while now, on various websites. It works well, but is a bit of a pain to set up initially. Once you had things working, though, it worked really well.
Version 4, on the other hand, takes away a lot of the frustration of initial setup, and you can get a first form up and running in minutes.
I did struggle with a mixture of 3 and 4, which is supported, but I couldn't get the form viewed on the front-end, so I removed all the Chronoforms components and reinstalled a "pure" version 4 instance, which worked really well for me.
The auto e-mail template function really helps to get an initial e-mail format going (was there one before?... I can't remember).
I still need to set up the database persistence and play with the v4's attachments handling (I had problems before with forms that allowed attachments, but with no attachment attached...).
It's obvious that a LOT of work has gone into this redesign, and for an early iteration (still in "Release Candidate" phase) it's already a very useful extension.