Nidesoft Video Converter does exactly what you would expect it to. It converts video between all popular formats.
It's most useful if you want to optimize and convert a video for a specific device or application - there are lots of conversion profiles you can choose to automate the settings. These include iPod profiles, Sony PSP and even Microsoft Zune players, so if you don't want to think about formats and video size you don't have to.
If you want to convert manually, there are most of the options you might want. Of course you can choose the output format, and the video/audio quality, and preview the conversion.
One thing Nidesoft Video Converter doesn't include is any option to cut your video, which is a shame. This means you can't just convert clips, or split a video into parts easily. This trial version also only allows two minute conversions, only really enough to test the quality of the converter.
Nidesoft Video Converter is a practical converter, but it's missing some useful features and is a very limited trial version.