I traded my BK SM250 for my xp5000 external. Haven't regretted it one day. The 5000 was on my system for 4 or more years without one single issue. Just did it's job day in and day out. Paired up with their auto neck cleaner, I'd just drain the cup every couple of days, for months at a time. And scrape straight mud off the underside of the cup lid when I would remember to clean it.
I couldn't get the 250 to stay dialed in for any length of time. Not knocking BK's , I really think the skimmer was just too much for my system (about 120 gallon in tanks, 320 TWV at the time). From what I've learned since, the BK's really need to be closely matched to their rating for them to be happy. The 5000 was also oversized for my system. But it was not as touchy- skimmed well, and without any of the overflow issues I had with the BK.
The BB pump puts out some nice small bubbles. I messed around with restricting the air feed like you do on the Deltecs with the Aquabees, and the skimmer went from putting out small bubbles to amazingly fine bubbles. But, it also increased the pump's electricity draw from its normal 60 watts to 95 watts or so. Figured it probably wasn't in the pump's best interest to run it so hard.
The neck extensions are nice also, if you have room for them.