The YF-19 is easy to transform compared to the YF-21. At one point the 21 "broke" into two pieces, just like the 19 will do when not held properly during transformation. I don't have pics to show where it came apart and it's very easy to put back together, but I did $hit my pants when it happened.
You do have to, kind of, break it's neck when going to battroid mode, but it's much easier and less scary than on the 19. That doesn't mean that it's less tight though. It's done in a completely different fashion.
Because of the small feet, it isn't as stable as the 19 in battroid mode, but the fact that it can remain standing with all that weight on it's back is a testiment to Yamato's enginuity.
When in battroid mode, the chest/cockpit can pivot up and down a bit because it isn't really locked down tightly. It's locked, just not very well. It's not like the 19 though, where it'll just come apart when you hold it upside down. The cowl can be pushed down slightly untill you hear a soft click, which prevents it from coming apart when held upside down.
It has ratchet joint on it's ankles, knees and elbows.
Once put together porperly, the gunpod will be held very tightly and the wrist doesn't cause the gunpod to be pushed to the side like on other VF toys.
The legs and arms will NOT come off easily for delimited mode. I tried to take the legs off to make the transformation to gerwalk a little easier, but they wouldn't.
The seat can rotate backwards and the cockpit can open in battroid mode exposing Guld. It's not as simple as on the VF-0 and I haven't figured out how to do it yet, but it says so in the manual.