I've had a Plexifairing 3 on my 750K4 for about one month now. I bought it for the same reasons you mentioned. It fits the bike very well both from the aspect of mounting as well as looks. Handling characteristics seem fine. The top is a bit below my eye level, so I can see over just fine when looking out ahead (I'm 6'3" tall).
I haven't ridden in the rain with it yet, so I can't comment on that. It protects me from bugs just fine; I stay bug free from my knees to the top of my helmet. I don't carry passengers often, so I can't comment much on their protection. But for the few rides my 9 year old son has had, he says he didn't feel any wind (he does have me to hide behind though). And the sissy bar (yes I have one of those) does not have any bug juice on it yet.
All of my rides have been less than 10 miles, but so far I haven't had any overheating issues even on 90 degree days. The bottoms of the lowers are near the middle of the fork boots (or at about the same level as the valve cover top); airflow to the cooling fins seems sufficient.
I guess my only real complaint is the wind noise on my head. It is pretty high when riding on a windy day (cross winds are the worse), but the noise is acceptable on calm days. My helmet has a vent on top that may contribute to some of the noise. I plan to adjust the shield angle forward a little to see if it alters wind flow over me for the better. Hope this helps you.