Bill uses Dragon Naturally Speaking. Leo says that Dragon is the king of speech to text and does a decent job transcribing what you say, but it's not perfect. Leo says that it'll get about 1 in 15 wrong, so he'll have to stop and correct it, which is kind of a speed bump. People with carpel tunnel use it all the time, though.
The different versions of Dragon Naturally Speaking are for custom dictionaries. The engine is basically the same. It will save him a lot of time though. Speech to text is a very hard thing to do, and he'll have to tell it how to punctuate. It also has trouble with homonyms. But it is getting better.
So what version of Dragon should he get? Leo says to go with the $200 version of Dragon Dictate.