They are great for quickly getting some appropriate soundbedding for your video. They loop perfectly which means you can extend them out as long as you want and add more loops directly to the Vegas timeline so that you can add other instruments or parts to compliment what you already have. They come with already built soundbeds as examples and the individual loops for you to use and build how you like.
If you have acid, you can easily build off of what VASST has already given you with Trak Packs.
The Sony collection is cheaper and you can pick more accurately what you want. I just checked out the Vaast TrakPak Vol. 3, supposedly "Techno" type music, and the sample was VERY lame, sounded like MIDI 16, and the general tone was poor.
There's a BUNCH of free loops on the VP9 Seminar Series DVDs, but the Seminars are not great. Glad I got it free.
there's never a good sounding totally adjustable completely customizable effortless music source ( at least not that I've found yet, after years of looking ).
The VASST TrakPaks are a good bunch of Discs to have in your library. They're not the end all be all audio series ( it doesn't exist ), but they are easy and fast, and can be used in conjunction with other audio tools for even more options.
I recommend them because I find that I can use them to be a foundation or a great accent to my audio.