BUT, you may not modify the script at all which can severely limit your flexibility. This is truly one of the better scripts available, but be warned that running a Yahoo-style site can take time. Support forum and FAQs are outstanding and incorporate a large number of hacks and mods. This is a relatively hard script to set up, but creating multiple test config files is good. Average difficulty in setting it up, but the ease of use factor is off the scale.
Some critical features are only available in the pro version for a fee.
Easy to set up with good documentation, but using the custom markup tags are a pain. Jury is still out on non-threaded messages. A little hard to install, as the variables are scattered throughout the script. Works allright once it is set up correctly, but only an average script. One major sacrifice is the lack of options for an item or the ability to set multiple shipping routines.