Summary: I would not buy this product again. My unit emits a constant electronic hiss even when all controls are in the neutral position. As far as I can tell, there is--incredibly--no switch that disconnects battery power when the unit is not in use.
Summary: I've been using the Sony M450 unit every day for several months -- ever since my previous Sony M430 finally gave up the ghost after 5 years of daily use. It works well, and gets the job done. Another reviewer complained of the lack of an "on/off" switch.
Summary: I found this Sony recorder perfect for making quick dictation notes, so much so that I constantly use it and may well purchase a second one as a backup. It is ergonomically well designed, the appropriate control buttons easily accessed, and doesn't attempt to look fancy like the Olympus models.
Summary: Perfect and excellent in many ways! I have been testing a number of these lately, and this is my number 2-ish choice in the field. My first is the 529V, but the 670V is perhaps the cream of the crop. It is getting tough to distinguish the top gunners and very best ones.