The mockingboard is one of those novelty items that is cool to pick up once you've collected several other items on your must have Apple II accessories list. At the top would be some sort of mass storage option like the original CFFA, or MicroDrive with CF attachment, or ideally the CFFA3000 on it's next run. It's an amazing device-- I'd highly advise it.
http://dreher.net/?s...ppleII/main.php
Click on Order Form on the left, and it will tell you that it's sold out but give you a link to get an email when he's ready to make another batch.
Apple II games that supported the mockingboard:
http://apple2.info/w...enhanced_titles
IIRC, the mockingboard wasn't interrupt-driven, so you had to attend to it in your main program loop. With everything that's going on in Ultima V, it's possible that there's stutter. I'll have to go back and play around with it to see. The other thing that could be happening is that if there's anything loading off of disk it would certainly cause sound to skip, as interrupts are disabled and everything is squarely focused on reading in data in a tight timing loop. I don't recall if Ultima 5 loads in an entire "zone" in memory, or if it quickly streams in new map data as you hit certain boundary point.
I have one of those Korean Mockingboards, as well as an original, and they both work well. I've seen the Korean one go for as low as $60 shipped in the past, so it might be worth waiting it out when demand is down and they start lowering prices. Collecting rarer Apple II items is an exercise in patience. The other thing you can consider is posting to comp.sys.apple2.marketplace with a WTB Mockingboard title. A lot of collectors, enthusiasts may have a couple and usually ask much fairer pricing than ebay. In fact, I've been able to structure trade deals with guys to include current hardware and/or other vintage systems/accessories for Apple II gear. So, if you have other interesting tech sitting around, put it in your WTB thread as a potential trade list and see what happens...
Good luck!
Rich