Very intriguing. As I understand it, Baji is often used by military and special agents over there, but I've always heard that Xingyi is still regarded as more of an internal style. I'm assuming there's much more to it than that. What is it useful for?
Baji actually has a very large internal component as well. Xingyi is great. Out of the 3 neijia schools (Taiji/Bagua/Xingyi) it's the easiest and simplest to master. The initial hand techniques or 5 element fists you learn are basically a lot like boxing. The mechanics work by coordinating a smooth forward hand and foot power. I'm gonna make a generalization here but for the most part it is a striking art, although large joint manipulation, takedowns, and throws are in there. Generally low kicks only. Xingyi teaches a small amount of techniques, like Baji, but teaches and encourages you to use all of them in very versatile ways.
For example here are the 5 fists:
They look like strikes but they all have different uses. Some can be transitioned into throws. some are used to simultaneously attack and defend.
Basically xingyi teaches the student to overwhelm the opponent in coordinated bursts of power resulting from proper body mechanics(the internal) and trained physical strength. It's a lot of fun, and really practical. Used to be used on the battlefield as an adaptation from spearfighting, and was employed against armored opponents. It seems simple, but there is a lot of depth to the mechanics and applications, kind of like baji.
It's linear, and aggressive. It's characterized as an internal style because there is HEAVY emphasis on proper mechanics and mental state. But i dont like using Internal/external as descriptors.