Hmm. Personally, I think the VF-31 is the best engineered transforming jet toy I've ever handled, but I also admit it's not my favorite design.
With some of the more-recent Valkyrie designs, it really doesn't look like it should be able to fly. For example, the YF-19 and VF-31, in Gerwalk mode, have their wings connected to the body of the jet by some very-thin wing kibble. I'm fine with suspension of disbelief, but if I think too hard about it, it looks like flying too fast or making too sharp a turn would snap off the wings. By contrast, the VF-1's wings (in Gerwalk mode) are connected to the body just as strongly as the connection in fighter mode, and so it looks like something that can actually fly and maneuver.
The insect-like design is...eh...an acquired taste. When I first saw the head of Messer's VF-31F, my first thought was, "What? I'm NEVER buying that...Waspinator-like...THING." Shrug. It's now one of my favorite Valkyrie head designs. I like the uniqueness. It still reminds me of Waspinator, but hey, Waspinator is awesome, so...shrug.
The large wing kibble is...eh...something I can live with. For better or worse, the Macross jet designs don't transform the wings, per se, but more like the wings fold away somewhere. (To illustrate: Studio Series Starscream transforms the wings in various places, and Starscream's robot mode doesn't have huge chunks of wing kibble hanging off it). The Valkyries that best fold away the wings (in my opinion) are the VF-17, YF-21, and VF-11. Pretty much every other Valkyrie has a huge wing kibble problem.
The VF-0, VF-1, and VF-2 have the wings folded up in the back like a large board. The animation cheats it with some mass-shifting wings, but even then, seeing such a large wing backpack on a toy makes it look very impractical. The YF-19 has huge wing kibble on its thighs. It looked cool in the 1990s, and it still looks cool today, but having it on a toy really shows you how impractical it is.
Seems pretty easy in combat to, say, grab the YF-19's wing kibble and tear it off the thigh and bam, it can't fly anymore. Heck, it seems pretty likely in combat to accidentally break off the YF-19's wing kibble.
The VF-31's wing kibble...eh...isn't that much worse than most other Valkyries. It's impractical, but not moreso than the VF-1 with a board behind its thighs, or the YF-19 with huge kibble that can break off or an enemy can grab. It looks to me that it's pretty easy to shoot at a VF-31, miss, but hit the huge wing kibble. Bam, can't fly anymore.
But.....ehhhh..........I'm pretty good at suspending my disbelief. I don't mind impractical designs if it at least looks cool. I don't need mecha to actually look like real combat machines (though that would be nice), as long as it looks convincing enough in the animation.
I grew up with Transformers, Gundam, and Robotech. Off the top of my head, I have no problem with Starscream, Blitzwing, or the Arialbots walking around with gigantic wing kibble on their backs. Shrug. It looked cool. Omega Supreme walked around with half-circles of train tracks on his shoulders, but it looked cool. Plus, have you seen certain Gundams? Wing Zero Custom's angel wings. Yikes! Seems like any sensible bad guy army should just bum-rush Wing Zero Custom and tear off its wings, but nobody ever does. My point is, I'm willing to look the other way if the robot looks cool and convincing enough, and I think the VF-31 passes that test.
Plus, the positioning of the VF-31 wing kibble kind of reminds me of the Hyaku-Shiki from Z Gundam.