I believe I saw in another thread some people asking about the BK3. The local Billiard Factory store here in Jacksonville received some in the first shipment (small commercial - they have a great assortment of cues, tables, and accessories!), and Erik the owner let me chalk one up and try it out.
Preface - In the past I've broken with my normal shooting cue, a spare Schon cue, a no-name brand cue, and currently own a BK2 with the weight bolt taken out. Typically use a power break from the side in 9 ball (pretty standard), about 25 mph with good control, any more than that and it gets crazy. Also will use softer breaks, cut breaks, etc. as needed but haven't perfected those as much as I would like.
Overall I liked the cue. It's lighter (about 17 ounces), the shaft is no longer radially spliced but has some sort of carbon fiber insert to remove weight instead. I broke 5 or 6 times with my current BK2 to get a baseline, then broke 8 - 10 times with the BK3. So not a long term test, but enough to get an initial feel.
Personally I liked the lighter weight, probably an ounce or so lighter than mine. Felt very solid at impact. I did not use the breakspeed app on the break (forgot), but it didn't feel or sound like it was noticeably any different, and I wouldn't really expect that when using the same technique.
I also purposely hit off center with both cues. The thing I liked about the BK2 was in the event you come through it on the left or right, in theory if you are bridging the same distance as the natural pivot point (which I believe is around 12" - 13") the ball will still go where aimed. I'm a decent player so I don't worry about that too much, but still nice for those occasional off-center contacts. Even though the BK3 is not using the same shaft technology, I still got good results when swiping across the ball or purposely using BHE with the same bridge length. So the carbon fiber must lighten it up enough to still give it LD properties.
Since I use my BK2 to jump on longer jump shots, I also tested the BK3 on these. I was able to jump a full ball from 12" - 14" away, about my minimum comfortable distance with a full cue. Was also able to easily get enough spin to draw the ball back the length of the table, same as my BK2, with good control. I would guess that the BK3 might be even better for this, since it's a bit lighter, but did not see any huge improvements in my small sample size.
So overall, I really liked the cue and it would be a great break cue for someone. The new shaft may be more solid than the BK2 shaft, where I have heard instances of the tip/ferrule just exploding at contact. For me and people I know that use the BK2 however there have not been any such issues, it's held up very well. Would like to see it with the sport wrap like on the BK2, although mine does not have that, just regular linen. However, I would say unless you are just tired of your BK2, or really want a lighter weight, the cues are similar enough that I don't know if it's worth the upgrade. Although in theory you could sell a BK2 in good condition for at least half the cost of a new BK3, so why not?