Here's my .02,
I had the Yam box on my '05 with the optional passenger back rest. Three main compliants;
1) The optional back rest didn't allow the passenger much space to lean back. This can become uncomfortable on longer trips. The backrest isn't very comfortable to lean up against, but it beats leaning against the box itself.
2) IMO, the Top Box made my FJR look a bit Goldwing'ish. Typically I'd leave my rear box at home unless I had a need for it, mainly because I didn't like the way it "bulked up" the looks of my FJR. But when you need extra storage space, it's nice to have.
3) The plastic mounting plate seemed a bit cheap, and definitely not lock-tight stable. Yam came out with a recall mod for this, but I never saw it. The mounting plate also permanently covers up the nice looking tail section of the FJR with a fairly ugly looking flat-black plate (can barely be seen with the box mounted). My mount never broke or cracked, but I would have felt better if the box had a more secure mount.
On the plus side; the color match was of course perfect. The Key/Lock supplied by Yam with key matching the igition key. No complaints on space... it held a lot of stuff. Full face helmet storage is no problem (but not two). I even stuffed a fair sized watermelon it there once!
Now I'm in the market for a top box for my '07. Here's my thoughts so far:
Yam Box for the '07... same as above. (Although I'd hope Yam sells it with the improved mounting plate.)
The Hepco Becker stuff looks like it's built like a tank, industrial looking, and IMO seriously ugly. The first time I saw HB's on a BMW I thought is was either a joke, or someone had gone nuts with their new welding equipment. On the plus side, HB's could cause serious damage to a cage in the event of a crash!
The Givi. No color match (although painting it has run across my mind). Attachment plate is steel which is good. Not sure if it allows an improved passenger "lean back angle" or not? Or what holes are necessary to mount the mounting plate? (Givi users?) Optional rear lights aren't very bright, but should be easy to modify to brighter LED's. More comfortable back rest for passenger.
So far I'm leaning towards one of the Givi models, and maybe get it painted to match. But it'll depend on what's involved with drilling up my '07 to mount the Givi mounting plate.
Oh, another thing to consider. Dis-mounting your bike with a top box (any top box), creates some interesting dismount procedures!
Good luck with your decision!