I just picked this up on eBay for cheap, and it's kind of interesting.
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The basic design is very similar to a Slimline, but the interesting part is that you can adjust the exhaust stacks. That part of the muffler rotates, allowing you to adjust the angle and direction of the exhaust pipes. I was messing with mufflers on an engine in a Balsa USA Force One (mid-engine pusher) and wish I had this one on hand at that time.I know... it's one more part that can come loose, but I have plenty of LocTite in the shop. :-)
Good flying, desmobob