Is it any where near the claims made for it my its DivX, Inc?

Its web page says: "DivX is the name of a popular new video compression technology developed by DivX, Inc. The format was developed to enable users to play and create high-quality videos in a fast and convenient way, while still maintaining the best quality possible. The DivX codec is currently the most popular MPEG-4 based codec because of its quality, speed and efficiency as well as the wide range of DVD players that support DivX."

I could be mistaken, but I think this Divx is the same Divx that came out years ago with "disposable" DVDs. They tried to get consumers to buy a disc at a lower price that had a "time limit" on viewing after initializing. They failed to catch on.

That could be the reason they are in a lot of DVD players- being a prior manufacturer. Since their codec is MPEG 4, I doubt they are any better than QuickTime. I have seen both and can't call a winner.

I think it's popularity claims are based on it being cross-platform like QuickTime, but mainly written for, and having better support on Windows.

It is the same in name only. This Divx has nothing to do with the disposable one.

Divx makes smaller files with about the same quality as H.264.

How do they make smaller file sizes than QuickTime when they both use H.264?

It's not H.264 but relatively close in quality to H.264, which is why the size is smaller.

Don't confuse MP4 with H.264. H.264 is one of the many variants of MP4.