The original saber was the first serious kite I designed. I'd designed a few kites before then, but I hadn't really intended for them to be great kites. I couldn't fly well enough when designing those to be able to tell what made a kite good, let along build that into a design.
I had gotten to be a better flier and had read/found a lot on design by the time I designed the first saber. I thought it was pretty great. As I became a better flier, I began to find some things which bothered me. Thus cam about the saber II. It wasn't meant to be an entirely new kite, just a refinement/evolution from the original.
I'll just refer to the original as the saber and the saber II as the II, just to be clear.
In precision they are fairly similar. The II turns slightly tighter and tracks a bit better. The saber was slightly slower. I think that the saber was slightly better for team flying at least at the level my team flies, but the II is better for individual precision.
The II has a wider range of tricks and executes them better than the saber.
Flat spins were a bit iffy on the saber, but on the II they are very nice. slots are a bit touchy, but look good. Taz machines are good. 540s are a snap. It's not like a cosmic, but it does them all nicely.
All the pitch stuff is there. Forward pitch on the saber was not really there, but on the II it is. Yofades are doable. Crazy copters are fairly easy. I'm not really good with either of those tricks on any kite, but I'm beginning to finally get them on the II.
Normal pitch on the II is a bit more rounded than on the saber. That makes the timing on waps slightly easier. It is also easier and cleaner catching the stoppers.
The comete and cascade are a lot less picky on the II. They are cleaner with a well tuned input, but the kite still will execute the trick without perfect timing and intensity. The kite doesn't stop dead in the air when given a bad input like the saber did on occasion.
The II actually does insanes and rolling cascades! For anyone who has seen me struggling with the saber trying to get those clean, you can imagine how happy I was when I finally got it tuned so that I could get them to work on the II

Fades aren't quite so set-and-forget as the saber, but they are still much more stable than most kites out there.
Overall the II is much more forgiving and adjustable. It can take many different types of inputs and respond well to them. It can trick slow and gracefully or fast and hard. Whatever the flier tells it to do. This holds true for any of the tricks it does, from lazies and backspins through to cometes and cascades. The saber was a bit more picky about that sort of thing.
The differences design wise are not very large. The lower leading edge has a bit of curve on the II which it didn't on the saber. The sail is a bit more shallow. The trailing edge was raised up a tiny bit. The frame was switched from the G-force/P200/5PT mix used on the saber to a P2X/5PT frame on the II.
I played around with some bridle mods, but I kept coming back to the original saber bridle so that stayed the same. Frame geometry and placement is all the same except for the standoffs.
The changes were slight, but as anyone who has done much with sport kite design knows, a little change goes a long way.