Most of the boss weapons are not that great. Some are worth using for making a cool weapon/shield, but I would say, by and large, using them for souls is a better use for them. Soul of Sif can be useful for the shield, and some people like the furysword from Quelaag. Otherwise, there are much better items out their for the most part. Some of the DLC boss weapons are pretty cool though.
Purge is really good for learning pretty basic ways to play heroes effectively in the current metagame. However, once you have a decent understanding of the game, you should watch merlini. He doesn't explain himself as much as Purge, but he definitely plays at a higher level, and exhibits really good efficiency that nearly anybody can learn from. He doesn't post on youtube much, but he streams pretty frequently, and the streams are always archived so there's that. Here is his stream
Also, don't go too deep into either players catalog, dota is an evolving game and some strategies become dated and/or nonviable as time goes on.