tl;dr: Five stars for the capabilities, four for the fit and finish. It's a great tool, but not without a few rough edges. (See note about iPhone 4S compatibility).
[UPDATE on iPhone 4S compatibility: I've heard many reports of people having trouble with the AR-4i and the iPhone 4S; my own usage indicates that there is one quirk with this combo: the wireless signals on my phone go away while plugged into the AR-4i. Example recordings with various firmwares below: