Alrighty! Just got my hands on the latest SS Voyagers and Leaders. However, the one that has won me over the most is Jetfire.
So, I was rather hesitant and critical about Jetfire when I first saw him, but after having him in hand for a day, I'm absolutely convinced. Jetfire is everything I wanted in the original Leader (albeit in a smaller package). Overall, he's much easier to transform than the previous Leader and everything but those two central panels that tab into the shoulders and engines hold together solidly. I'd even argue that the kibble is much better on this one.
While the fit and finish are subpar as per other figures in the Studio Series line, the bot mode is excellent. The transformation is really fun, smooth and impressive. I love how the jet mode folds in on itself multiple times to create the bulk of the body and I adore the fact that the thighs are actually formed from the jet mode engines unlike the previous Leader (they even sit accurately within the nacelle!). I'm still not that big of a fan of the faux cockpit head, but after knowing that Jetfire accurately parts-forms to combine with Optimus, it softens the blow somewhat.
Speaking of which, yes! Jetfire does indeed combine with SS Voyager Prime!
...and it's amazing. Thank heavens they decided to go with parts-forming. Not only is it accurate to the movie, the combination gimmick does not take away from either figure much at all. The locks that secure Jetfire's limbs together when he's his own figure are brilliant. It's a clip system that holds all the parts together in bot/jet mode solidly but is still easy enough to disconnect for parts-forming when needed. In Jet Power Prime mode, everything is just as solid, though I'm slightly worried that Prime's leg joints (hip and knees) will not hold up over time as they aren't ratcheted. As for now, they're rock solid and almost too tight for when posing him alone. While the articulation in combined mode is mostly unhindered, it kinda sucks that the ankle tilts are opposite as Jetfire's legs are reversed for the combination.
Note that the instructions are utter garbage. Not only does it not tell you how to transform the cannon at all, but you can tweak the figure a little to get it looking much, much better. For instance, the bar behind Prime's head can be angled back. This not only tidies up the silhouette, but it also holds the rear wings/fins in place. Speaking of those fins, as can be seen from the above pictures, they can also be splayed open for a far more dynamic and movie-accurate look. It's a pretty nice touch that Prime's back kibble form secondary fins.
For the cannon, there is indeed a proper way to transform it. Upon close examination, the arms and flaps both have places to peg into.
All in all, thus far, Jetfire is my undisputed favorite Studio Series figure. So poseable, so much more accurate than the previous Leader figure and so full of character! All that on top of a much-improved combining gimmick! Now I only wished that they had put more effort into the Voyager Prime. I still don't get the necessity for the inaccurate leg transformation and the faux chest. In addition to being inaccurate, in my opinion, it's needlessly complex and fiddly for a Movie Prime and is as light as a feather. If you ask me, I'd only buy Prime solely to maximize Jetfire's playability. That's how great Jetfire is.
First they barely finish transforming a figure, now they give them a different figures accessories 
I want to love this Jetfire so much, but that beard when he's displaying that awesome SR-71 Blackbird mode can't fly. I can't un-see it, most of the rest of the bot being kibble under the jet I can ignore as elements can be kinda taken a landing gear, just not that beard. 
